LIGHT CABLE ROAD CONSTRUCTION
by Frank Van Vleck

This article, from Transactions of the American Society of Mechanical Engineers, American Society of Mechanical Engineers, 1891, describes in some detail the theories that the author, Frank Van Vleck, followed when designing and building the San Diego Cable Railway. The author presented it at a meeting in Richmond, Virginia in 1890.

From Transactions of the American Society of Mechanical Engineers, American Society of Mechanical Engineers, 1891.

THE main objection urged against cable roads for small cities has been the almost prohibitive cost of construction. Advocates of electric traction have even asserted that cable roads could not be built as a single-track system, thus making the cable road a luxury only for the metropolis. In the far West there are a few good examples of single-track cable road work, and the object of this paper is to present another case where a single-track cable road has been put under construction -- a road in which the main aim has been to combine the elements of a thoroughly good plant with such economy in cost as would warrant the erection of such a system in a town of between thirty and forty thousand inhabitants.

In these days, when it is almost universally recognized that for the purposes of intra-urban traffic the emancipation of the street-car horse is at hand, it is asked and demanded, which, then, shall be our steed for our new rapid transit, electricity or the cable? Electric railways, under the enterprising energy of special corporations formed to develop them, have made enormous strides, and their success has been well merited ; for, in truth, it must be said their attainments, both mechanical and electrical, have been almost phenomenal. Yet there are some things the electric railroads cannot do, or cannot do, as at present constructed ; notwithstanding some amusing claims of the electricians that certain grades can be ascended which the steam-railroad men know to be impossible of ascent under all conditions of track and weather. The writer, although connected with the development of the cable system, cannot but conclude that the day of usefulness for the cable on the level is forever gone, and that the electric road stands the champion of the field. When the ascent of steep hills is to be undertaken by any street road, then the advantages of the cable over any other means of locomotion are apparent. Representatives of the electrical companies have claimed, and even attempted, grades ranging up as high as 16 per cent, for their motors, and have repeatedly asserted that, when using the return current by the rail, the tractive effort is increased by the electric adhesion between rail and wheel. The amount and character of this adhesion has not as yet been as fully explored as the demands of tramway engineers would wish, and with the electrical engineers themselves this feature has not been made as much use of as the merits of the discovery would seem to warrant. Therefore, in the present condition of the system, it would appear unwise to assume that any electric-motor car could have any greater capabilities of ascending hills, or for traction, than steam-motors with same conditions of weight, wheel base, and track.

Most of the cities of our country are located on the level, and as such are eminently adapted for electric railway work, while often other cities have the misfortune to be built on hills. He would indeed be a bold projector who would claim the possibility of ascending some of the San Francisco hills with any form of traction locomotive, some hill streets in that city being entirely given over to the cable roads, as no vehicle can with safety ascend or descend. The inclines of either the Hoboken Elevated or the Brooklyn Bridge would also be a difficult ascent under all loads and wet tracks.

Space has been taken for allusion to the relative merits of these two systems, as the consideration of them has been an important feature in the San Diego Cable Railroad, about to be described.

This San Diego franchise was first operated as an electric road, and as such continued in operation for about a year. Deficiencies of construction, improper design, inability to ascend grades with any reasonable speed, or at all, and large leakages of electricity and consequent loss of power, compelled the company to cease operation at an early date.

The electric road's franchise and equipment were then purchased by a company purposing the adoption of the cable system. This new cable road has just been put into operation, and its description constitutes the subject-matter of this sketch.

Before breaking ground the officers of the road had already determined for the engineer that the road was to be a single-track system, and was to be constructed with thoroughness, yet at a cost which was to be materially less than that considered moderate for other roads. For it must be understood that the city of San Diego is of such size that neither heavy traffic nor receipts could be expected for some time to come. It therefore may be observed in the following descriptions that, while many of the best elements in cable engineering are employed, the designs also show that the items of cost have in each case been pared down to lowest figures. In many cases new departures from usual practice were adopted for economy, yet, when such new designs have been completed and installed, they have been found to be more satisfactory than the older forms.

It will be seen that the construction of a single-track system produces a complexity of design which is practically a simple matter to the double-track system -- a case where the apparently simple is yet the most complicated.

The double-track roads have but one cable moving in their conduits, and moving invariably in the same direction. The underground passage of grips and the movements of surface cars are therefore positive and in the same direction. But in the single-track system, although it may be the essence of simplicity in the streets, yet underground its ways are devious. Two cables demand attention, each hurrying in opposite directions, yet side by side. The grip likewise must be capable of holding to its proper advancing cable and not to the other. Curves present a maze of difficulties. For the uninitiated can see that two cables, each running in opposite directions, cannot pass around the same curve-pulley at the same time.

The backbone and foundation of a cable system is the road substructure, the form of the iron yoke binding all the rails and shaping the conduit, and the concrete foundation. The influence of a fine California climate had not a small share in the determination of the iron which forms the yoke, for in this part of California frost in the ground is a contingency which engineers never consider.

This yoke is shown in Fig. 1. The positions of track-rails and slot-rails are as shown. The form of the central conduit was determined by these considerations : Two cables must traverse the entire length of the conduit. They must not be so close together as to chafe each other in oscillating sideways, nor so close as to touch the rims of the sheaves carrying the opposite cable ; nor, again, must they be so far apart as to swing against the concrete sides of the conduit, or so close to those sides as to render difficult the passage of the grip, which must embrace the cable from the sides. The sizes and position of the sheaves carrying the cable also had their claims. Drainage had to be provided below all, in order to allow free passage of water and dirt below both cables and sheaves -- for it must be said of Southern California, with somewhat of the reputation for being

during most months in the year a semi-arid region, yet it does have the accompaniment of rain sometimes during the winter months, and when it does so rain vast volumes of water fall in short spaces of time. In such cases cable roads may run like small sewers, and not to make provision for water would be ruinous to the cable ; for the grit thus carried about and into the strands of the cable doubtless is a prominent factor in decreasing its life. Finally, the cross-section of the grip must determine the main form of the conduit, for this grip must pass every point of the road and must be capable of taking the rope only at the proper level, and taking the correct moving cable according to the position in which the car is headed.

Therefore, in a road of this kind it was necessary that, even before any other mechanical details were determined upon, the grip itself should be designed, or, at least, the form of its cross-section unalterably fixed.

The form of conduit thus derived will be observed to depart from the usual practice of double-track roads, in that the grip necessitates an angle in the side of the conduit where ordinarily is but a straight side, as seen at A, Fig. 1. In the matter of the gauge between rails the directors of the road simply consulted expediency, nor did they hunt up any absurd regulations, if such existed, requiring street lines to conform to some old rustic's idea that street tramways should always be made to conform to the supposed gauge of all the local wagons and carriages. Many cities have enacted such ordinances, with the thought that it was the right and privilege of all vehicles to have the pleasure of riding in the " flats " of the street rails. Thus in various cities of the country do we see gauges running from six feet to three, and even less. It may be that the "battle of the gauges" is yet unfought for tramway work. It almost appears that the standard 4' 8 1/2" has not a proper raison d'ętre for this class of construction, which is scarcely comparable with steam railway work, and rarely exchanges traffic with such roads. Therefore this San Diego road, following the example of numerous other cable systems, promptly decided for the 3’ 6" gauge, and would even have decided for six inches less and reaped further benefit of still diminished cost of construction, had they thought that public sentiment would look with favor upon such a narrow gauge in a city already compassed by the wider standard gauge. The outside width of the yoke being thus determined by the gauge, the yoke as completed is somewhat of a V form with the bottom rounded. The conduit or tunnel extends to within six inches of the bottom. From the figure it will be seen that the tendency of the yoke to close is resisted mainly by the metal in the cross-section at the bottom of the conduit ; this, therefore, was given as much iron as could be conveniently done in a yoke of so light a weight -- 150 pounds.

The rail used is of twenty-five pounds section, and although light for cable road service, yet, as large quantities were left as an heirloom by the former electric road, it was decided to use it for whatever might be its term of life, and then, if the traffic so demanded, lay a heavier rail. T rails can never be regarded as the best tramway section to lay in a city street, yet where the paving outside is close to the head of the rail, and the paving inside is at the height of the top of the rail, with but a flange-groove between rail and paving, the objections to the T section almost disappear. This was easily arranged, as the paving between rails on the entire road is of asphalt, or what is more specifically termed, at the Pacific, bituminous lime rock.

The slot-rail (Z, Fig. 1) is a special section rolled for this road, the desire here being to secure one of the lightest possible forms, one which would be inexpensive to adjust, and one which should avoid what with many other roads has been inevitable -- the use of paving-plates. What are known in cable construction as paving-plates are strips of cast or wrought iron extending from yoke to yoke, near the slot-rail, to prevent the concrete from being pushed from its sharp angle into the conduit or tunnel.

This matter of paving-plates alone is one which may affect the cost of a mile a thousand dollars or more.

A few cable roads, on the ground of pinching economy, have attempted to save a considerable amount by the abandonment of concrete as a binding medium to hold yokes and roadway together. Although this saving may be material in first cost, yet the expenses of general repairs and the hosts of nuisances of bad alignment and closing slots render it unsuited to what aspires to be a satisfactory system. Therefore it was early decided to use concrete throughout this new system, but not in such large cross-section as would require a large outlay. The external bounding of the concrete cross-section follows the outline of the yoke, except that at the bottom the concrete is run three inches below the yoke for the purpose of forming a better foundation, and a bond between the contiguous blocks of concrete between yokes. This concrete was formed with the proportions usual to many roads, three parts sand, six of broken stone, and one part of best imported English Portland cement. The mixing was in all cases done on the road, beside the work, and at once thrown into position between the yokes in the trench, and then thoroughly tamped. Yokes were spaced at four feet centre to centre, and at every tenth yoke was placed a "pulley yoke," this being such a one as is shown in Fig. 1. The plain yokes do not have cast on their conduit curve the two brackets shown at B, B. In other singletrack track cable systems it has heretofore been the custom to place a pulley or rope sheave on one yoke, and on the next yoke another pulley for carrying the opposite-going cable. This requires two yokes to be prepared for the reception of the pulley-boxes, and then on each yoke two boxes are to be attached, usually by bolting, and brought into proper alignment. To make each of these two pulleys with their four boxes accessible from the street required either two manholes through the paving or one long and expensive manhole spanning from yoke to yoke.

By the system here employed for the first, both pulley shafts are brought close together, and can therefore be carried in a single frame (see Fig. 2). This frame passes around and carries both pulleys. Having them both in the same frame, whenever the frame is adjusted to proper position then are all four bearings in correct line. This frame is simply passed in over the brackets attached to the yokes until it comes to its mid-position, when a depression in the frame drops over the bracket ; if, then, a thin, wedge-shaped piece is driven in on each side, the frame is rigidly held to place and can neither back out nor move forward.

Another advantage of this frame-carrying device is that the oil-box on one side embraces both journals ; thus, one oiling oils the two shaft ends. It also affords a large receptacle for containing the oil or oil-waste, or "dope." The whole thing is also readily accessible from one small manhole in the street.

The small carrying sheaves (Fig. 3) are ten inches in diameter with a three-inch face, and are mounted on cold rolled steel shafts about twelve inches long. The sheaves are of cast-iron throughout. To the uninitiated in cable work it appears strange that cable engineers persist in letting their splendid steel cables wear themselves out by passing along and around wheels whose surface is hard cast-iron, while theory would seem to dictate the invariable practice of using a softer material for this rope to

pass about on. Some roads do, indeed, use sheaves with grooves filled with Babbitt or wood. Whether such use has lengthened the life of the cable appears to be doubtful, while its manifest disadvantages have been often too evident. The great disadvantages are greater wear and consequent frequent renewal of the softer material and the greater difficulty experienced by the soft wheels taking the "lay of the rope." This latter is an effect which all cable men seek to avoid. When a cable is considered in its best condition, its depressions between contiguous strands are uniformly filled with tar or pitch, so that the appearance of the cable is not unlike a well-tarred gas-pipe. In this condition it resists better the wearing action of sand or grit, which may chance in the conduit, and is far smoother in its action in passing through the jaws of the grip. When a wheel or sheave takes the "lay of the rope" it has formed in its groove the matrix of the cable or the opposite of the space between strands. This matrix gradually increases its resemblance to the space between strands, with the consequence that it pushes all the tar from between the strands, thus setting back the cable to its original naked condition. When such a wheel or sheave is found it is promptly taken from the road and thrown away, or the groove, if the stock in the rim permits, is re-turned.

The manhole through the paving whereby the oiler has the opportunity to perform his duties is perhaps smaller in this road than any other. As this is a detail of constant repetition

on the road, it is evident that five or ten dollars saved in its construction means a comfortable saving at the end of the road. The size is only 12" x 14", yet a small man or youth can pass through it and along the conduit of the road. During the progress of construction on many roads it is desirable or necessary that a man should pass into the conduit for the purpose of bolting up parts or attaching sheave supports, but on this road all can be done from outside, even to the attaching of the pulley-frames, for neither do these nor other internal devices require any work of bolting. Practically, then, the main and only use for these manholes is for oil-holes. The manholes and frames are shown in Fig. 4, and although they are but made of cast iron, yet they are so braced that they give maximum strength. In fact, not one of them has yet been broken by heavily loaded wagons, by fire-engines, or road rollers.

The line of the road in two places crosses deep gullies, in one of which the roadbed is some seventy feet above the bottom of the ravine. In both of these cases high wooden bridges have been built. As it was possible for vehicle traffic to come upon these bridges, it was decided not to leave the space between rails open, and accordingly the problem was presented -- to carry the slot-rails in the centre and to carry any load which might come between rails, and to preserve accurately the gauge distances between all rails ; and, finally, to have the yoke so formed that it might be afterward filled with concrete, should the ravine be

filled and graded. The yoke devised for this purpose is shown in Fig. 5.

This yoke was given a little more metal through the central section in order to resist closure, should heavy loads come upon the slot-rails, and in this case it was the more desirable as no concrete was here used to bind or to strengthen the yokes. The ravines over which these bridges pass will probably be filled and graded to the proper street-level later, when these yokes can be arranged for the usual track work by attaching a triangular bracket to each side of the yoke and under the rails, and then filling in with concrete in the usual manner.

Scarcely any street railway-system can be built without curves, and these to the cable system are perhaps a necessary yet an unmitigated nuisance. Costly to a degree which make stockholders sigh, they are a source of endless care and anxiety to the management ; and not content with that, these crooked tracks still demand further extravagance by eating the life from

the cable. Curves are bad enough for the double-track systems, but with a single track the difficulties increase. For how shall these two cables, each moving in opposite directions, be taken around the horizontal curve-pulleys ? For neither can both ropes be carried on the same sheave -- for no wheel revolves in two directions at once -- nor can alternate pulleys be used for either rope. Practically, there are but two methods for accomplishing this feat. The method first made use of was to carry one rope at a higher level than the other, and have it pass over curve-pulleys above the pulleys carrying the opposite-moving rope. This required that the gripman, when having the lower rope, must invariably release his rope from the grip, and then let his car "float" over the curve either by momentum or gravity. Usually these curves were located on a grade in order specially to make use of gravity to carry the car around. In these cases, when the gripman did not release and drop his rope, the grip, from its construction, carried the rope into the wrong pulleys, and trouble ensued at once. To add to the difficulties, after passing the curve provision must also be made for picking the rope up, for grips as usually constructed have not the power to go down after the cable. The other solution of the problem is to separate the ropes and to construct the curves as double tracks. This was necessary in the road described, as no curve was on an incline which could be depended upon to float the car over by gravity. As a single-track road requires a certain number of passing places or turnouts, these double-track curves were so arranged on the line as to serve this same purpose of passing places. Fig. 6 shows in diagram the manner in which one of these curve turnouts was arranged.

This is a right-angle curve, where the turnout is located on the inside of the curve. It will be noticed that the inner curve is not included by the same angle as the outer one. This was caused by the fact that this arrangement would give a short piece of straight track between the ends of the inner curve and the switches, thus doing away with a number of curve-pulleys and their corresponding disadvantages. The turnouts, whether arranged as thus indicated for the curves or whether constructed at the side of the straight track, invariably have passing through them the moving cable to insure that the car will always be able to move in its proper direction. The entrance to a turnout on the straight is shown in Fig. 7. This diagram also indicates the manner in which the slot is deflected from the centre line in order to insure that the grip will not strike the curve-pulleys. At no point on the road between termini, except at power station, does the grip have to let go the cable. Thus at all points, whether on curves, turnouts, or switches, the car can always retain its rope. This releases the gripman from a vast amount of responsibility and insures greater safety for the passenger traffic.

The form of yokes for the curves were designed with many differences from the yoke required for the straight, as the curve demands features of strength which the other need not possess.

The form of curve-yoke is shown in Fig. 8. The main outline is made in the form of a square, for the purpose of strength, and for holding a greater body of concrete than such a depth of yoke would if made in the V form. For if concrete in sufficient mass has not been put in a curve, the curve has been known to be pulled either up or out of shape by the heavy tension of the cable. The conduit, it will be noticed, is shallower than the straight yoke ; this is due to the fact that each alternate curve yoke is fitted with a wooden block whose top surface is but a short distance from the cable. As this impedes the flow of water through the conduit, it was decided to form the channel-way for water under the frames for the pulleys, where it might have unobstructed flow, and which space of necessity is left unfilled with concrete, for the action of the curve-pulley. The yokes as thus constructed are strong, and when concreted up form a rigid construction capable of withstanding any of the strains to which curves may be subjected. The frame which carries the pulley is attached between two brackets cast on the yoke at A. The grip is prevented from being drawn against

the pulleys by the grip-guard at B, against which the grip slides in its entire passage about the curve. The grip, previous to its entering the curve, is deflected three inches to the outer side, by a deflection made in the track-slot to that amount. This permits the cable to run directly from the tangent to the first curve-pulley in its own proper line, while the grip by this means is carried to one side enough to clear the pulleys, and the strain imposed upon the cable by this bending is taken by the grip-guard mentioned. The curve-pulleys are carried between each yoke by the special frame of wrought iron shown in Fig. 9. These pulleys are of cast iron with chilled rims, the width of rim being but 3 1/2 inches. This narrowness of rim is made possible by the fact that the rope is lifted but 3 inches by the passage of the grip, and, consequently, after the grip has passed the rope falls to its mid-position on the sheave. Even should the rope come higher it could not remain above the rim of the sheave, due to the presence of the grip-guard. As these sheaves are so small in width it is deemed cheaper to renew the whole sheave when worn than to use a larger pulley with a renewable tire. The diameter of the wheel is 22 1/8 inches on the pitch circle, thus striving to attain what the present best cable practice deems most desirable, as large curve pulleys as possible, and spaced

as closely as yokes permit. The distance from pulley centre to pulley centre is about 3 feet. The details for keeping the journals of these pulleys under a sure condition of good lubrication will be seen from the drawing. Above each pulley is placed in the paving of the street a manhole of sufficient size to permit of the removal of the pulley and its frame complete.

Perhaps the one thing about which the whole design of a cable road hinges, from roadway to rolling-stock, from curves to turnouts, is the form of the grip. The grip early decided upon was a modification of the "bottom grip," now in most general use in San Francisco -- a form which has been known as the San Francisco grip ; but as so many of the grip constructions have emanated there and have received the same appellation, it is now no longer a designation of any definiteness. Single-track roads have heretofore used the grip known as the "side grip." But for its manifest disadvantages, it would have been adopted in this new work. It does, however, have one feature recommending it to single-track work -- the ability to grasp the cable at the side -- for, necessarily, where two cables are in the same conduit, each must be at the side of the centre line. The bad features of the grip for this new plant were that it lifts the cable too high from the normal position which it occupies on the carrying sheaves, thus requiring a deeper conduit ; and its general unmanageableness when the cable has to be dropped and picked up. For in case the gripman by carelessness neglects to let go the cable at the proper time, the cable must either be torn or the grip demolished, and there is no escape from the alternative. At certain points on the road, as at power stations and turn-tables, the cable must plunge down, and for the grip to " hang on " requires that something must give way. The " bottom grip " offers the two advantages that it lifts the cable but little from its normal position, and that in cases of neglect it can spring open itself before doing great damage either to itself or the cable.

It was found on investigation that these San Francisco bottom grips had never been constructed on the side, for the purpose of taking the cable, as would be necessary in single-track work; accordingly, the writer designed the form of grip shown in Fig. 10, which is possibly the first attempt to construct this grip as a side and bottom grip.

Fig. 10 shows the general view, and Fig. 11 a cross-section through the grip-jaws. The shank plate A, below the slot-rail, passes through the upper part of the grip-box B, and carries the hinge-piece C. This hinge-piece has hinged to it the two jaws J, J; these jaws constitute the vice for gripping the cable. The special surface which grasps the cable is an inserted piece, usually of cast steel, dovetailed in the inner side of each jaw. The softer metals are often employed for this purpose, but, as the wear is so rapid and the renewals so frequent, the expense counts up to such an item that it is considered as good practice to put in hardened jaws and assume the possibility of a trifling greater wear upon the cable. The pressure upon the jaws causing

them to tighten upon the cable is produced by pulling upward on the outer side of the jaw a steel roller E, carried in the bottom of the grip-box. This grip-box is fastened to the two side shanks of the grip, and when the gripman pulls up his lever to the position for tightening, this movement causes the two side grip shanks to be drawn upward, thus by means of the rollers causing the closure of the jaws upon the cable.

This subject of grips is perhaps one of the most important ones in cable road management, and, like many other important details, is treated differently by different companies or engineers. Each road is found to be using its own device. The relative merits and demerits of each have caused considerable discussion, and yet offer a fruitful field for engineers to balance practical considerations against theorized advantages. Thus, for example, may be drawn out the case of the ingenious device of Colonel Paine, on the Brooklyn Bridge, contrasted with the direct rubbing grips of some other cities.

The rolling-stock for this road presents a few new features, but such perhaps as, in detail, would only be interesting to tramway men.

To those of the East it may be well to mention that the cars are equipped entirely with trucks, as it is found that a much larger and more convenient car can be built than is possible for one which is simply to ride on a comparatively inflexible wheel base of four wheels. As the wheel base of the trucks is only four feet, it is seen that curves of extremely small radii can be turned with ease. The height of car body is no more than is usual with the standard Eastern build, yet the trucks are given a free angle for swinging and the wheels do not necessitate ugly covered holes in the car floor. This is made possible by using smaller wheels than the four-wheeled cars. As neither draught considerations nor tractive adhesion need be regarded in cable work, wheels, therefore, of smaller diameter are not only possible but desirable.

The limitations set by the directors were not unusual -- a power house and equipment to be supplied at mininum cost, yet as designed throughout to be not only satisfactory, but, if possible, ornate.

The engines at once contracted for were of the Corliss type, one being 18 x 42 and the other 22 x 42. Compound engines would have been considered were it not for the fact that the expense of the engine plant was already heavy, due to the necessity for two separate engines, where but one was in use with the other in reserve. High-speed engines might have been desirable for their well known advantages, but in cable work they are practically inadmissible, as the reduction in speed must be considerable, in order to bring the speed down to the comparatively slow speed of the cable. Even with the slower-going Corliss, in the case before us, the reduction in velocity ratio between engine-shaft and cable-winder was as four to one.

The steam-plant of the power station consists of four steel shell boilers, 62" x 15', arranged in batteries of two. Tubes are 4" in diameter. The smoke flue is taken over the tops of the boilers to the rear wall of the boiler room, and thence to the stack, which is located on a higher level in the car-yard of the power house. The boilers are capable of furnishing steam at 100 pounds, and not more than two or three boilers are expected to be in use at the same time, thus affording a reserve for alternation in case of the break-down of any one of them.

The disposition of engines is such that either one can be coupled to the intermediate transmission shaft. This intermediate

shaft is shown at A in Fig. 12. This figure also shows the general skeleton on which all the details of the winding machinery have been built. Of the two principal methods of driving cable-winding machinery, one by gearing, and the other by belting, the latter has been adopted as being the one nearest fulfilling the local requirements. The belting from the engine-shaft to the main winding-drum is effected by means of cotton ropes. This system of power transmission, although so much despised by some engineers, yet for cable work offers decided advantages. Foremost of all, it is noiseless, which is more than can be said of most cable plants furnished with cog-wheel gearing, but in justice to later builders of gears it must be said that some of the recent large-cast gears are models of quietness and perfection. Cotton-rope transmission also has the one greater feature of ease in renewing any part or parts without disturbing the action of the remainder. Any rope can be cut out, or a fresh one turned in, while the machinery is in motion. The foundation plan for the winding machinery is perhaps rather new in this class of work. The main foundation consists of a mass of concrete, represented by the sectioned portions of the drawing. Each end is raised to a height sufficient to receive the ends of the iron-work of the frame. This main frame of the " winders " is built entirely of heaviest sized sections of 12" steel I beams. The use of steel thus for foundation beams was found not only to conduce to most satisfactory economy, but to a lightness of structure which would be impossible with cast iron, and rendered possible a form of design which brought all parts of the mechanism to view at a glance -- a feature of no small importance when directors had requested that all mechanical movements of the power station should, whenever convenient, be made visible to the public.

The diameter of the cotton-rope drum on the engine-shaft is 6' 3". The large driven drum is 25 feet in diameter, thus reducing the engine revolutions four times. The shaft B, on which the 25-foot drum is carried, is prolonged at each side beyond its bearings, and carries a 12-foot diameter cable sheave on one end and a 16-foot diameter cable sheave on the other. Midway between the engine-shaft and the large drum shaft is placed the shaft C, carrying the cable "idlers."

The method of pulling the cables can now be seen. The line marked "city cable" is at the right hand of the drawing, and its motion is in the direction indicated by the arrow. This cable is drawn up on the cable sheave in its first groove, the cable passes but half a revolution about this sheave, and is carried off at the top to the idler sheave on shaft C. The centre line of the groove in the idler wheel is half the groove pitch behind the groove in the other sheave, as will be seen in a following drawing. After passing half a revolution around the idler it again passes to the other sheave. This constitutes one wrap, and on roads performing ordinary service from three to four wraps are considered necessary. After the last wrap the cable

passes to the tension carriage, and thence is returned to the road. The city cable, it will be noticed, is wound about sheaves which are 12 feet in diameter, the speed of the engines being so proportioned as to give this cable the uniform speed of eight miles per hour. The " suburban cable," on the other side of the foundation, passes to sheaves on the same shafts which are 16 feet in diameter. Thus, with the same shaft and engine speed it will be observed that a speed of twelve miles per hour is given to the cable. As horse-cars average but six to seven miles per hour, this twelve-mile speed is far better rapid transit.

Some of the details of these large wheels and forms of grooves

may not be uninteresting. The method of binding up the large 25-foot drum is shown in Fig. 13. This drum is composed of ten separate segments and ten spokes bolted together. Recourse was again had here to the exercise of economy, and all parts were proportioned as lightly as strength and stiffness would warrant. A surprising amount of metal was saved without sensible decrease of strength by simply grooving out the backs of the segments to correspond to the ridges formed by the rope grooves on the front. The form and angle of the cotton-rope grooves will be seen on reference to Fig. 14. The form of grooves carrying the cable, or the grooves on which is thrust the entire work of pulling the cable, is represented in Fig. 15. The driving sheave is shown with five grooves and the driven sheave with four. This difference is necessitated by the driving sheave having the cable touch

it in the last groove before the cable passes to the tension carriage. It will also be observed that both driving and driven cable sheaves are provided with larger and deeper grooves for carrying two cotton ropes. The driven sheave has here been termed an idler, but, properly speaking, it is not an idler, and to relieve it from its reputation of idleness provision has been made by means of these grooves and cotton-rope transmission for it to do its share of driving effort. Two cotton ropes pass from the driving sheave directly to the driven sheave, and, as the latter is one-fourth of an inch smaller than the former, it causes in the cotton rope a tendency to hurry the driven sheave more than it would do if the diameters were equal ; and, as the diameters of the cable grooves are equal, this tendency then amounts to a pull upon the cable, hence the idler is caused to perform a certain appreciable work. This ingenious method of utilizing

the idler for work was first introduced in the Los Angeles Cable Railroad systems, and was originated by Mr. W. R Eckart, of San Francisco (Member of the Society).

The tension carriages or the devices for taking the slack from the cable may also present some novel features. These tension carriages may be classed in three groups. The first and oldest form, and the one now considered most unsatisfactory, was an arrangement whereby the tension carriage, carrying its own or added weight, hung in a loop of the cable, so that its movements took place in an inclined plane. The second class of tension devices consists of the carriage placed in the loop, but travelling on a horizontal tramway, the weight, hanging in a pit, being attached to the carriage by cables or chains ; the great disadvantage of both of these systems being that,

should the cable suddenly give way (which is a rare but still possible occurrence), the weight and carriage instantly rush to the end of their respective ways to their own demolition.

The third class of tension carriage consists of a double carriage, one moving upon the other. The upper carriage holds the cable sheave. The weight is attached by chain to this carriage, but this chain passes over pulleys on the under carriage. The weight is therefore carried by the carriages themselves. Usually this weight hangs suspended under the carriage while the carriage itself travels along a runway or trestle. In the San Diego pattern, which is adapted from the last form, the weight hangs within the under carriage ; thus the tension carriageway need only be an ordinary track laid upon the surface of the floor or ground.

The architectural appearance of the power station is seen in the general views as shown. Although the building was by no means expensive, yet the desire was to have it of such tasteful appearance as would not render it an eyesore to the residence part of the city in which it was located. The architect, Mr. Wm. H. Hebbard, having had valuable experience in designing the architectural details of the three ornamental and most satisfactory power stations of the Los Angeles Cable Railway Company, came to this San Diego work with a complete knowledge of what such a building demanded, devoted to boilers and engines, to rolling-stock and repair shops. Views of this power building are shown in the diagrams here given.

Prof. Jos. E. Denton. -- I would like to know what the grades are which this road can handle and is handling?

Mr. Frank Van Fleck. -- In reply to the question of Professor Denton, it may be said that cable roads may be operated over any grade, even to a vertical, and attention may be called to the fact that ordinary passenger elevators are but vertical cable railways. The grades on the road in question are but eight per cent, on the steepest incline, with a number of short grades of but six per cent.

* Presented at the Richmond Meeting of the American Society of Mechanical Engineers (1890), and forming art of Volume XII. of the Transactions.

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