November 5, 1886.] 



SCIENCE. 



419 



wheel on the line-shaft, which is a foot in di- 

 ameter and about fifty feet long. The line-shafts 

 of both plants may be coupled together, so that 

 either engine may be used to drive either section. 

 Each section carries two pairs of cable-drums, 

 either pair of which may be thrown into or out 

 of action by clutches. Thus either engine may be 



used to run any of the four cables shown in the 

 engraving. The section at the right actuates the 

 duplex cables running out Tenth Avenue ; that on 

 the left will be used for the 135th Street branch 

 of the company's line. 



The cable, coming from one of the guide- pul- 

 leys in the street, shown at the right of the en- 



FIG. 10. 



graving, passes several times around both cable- 

 drums, thence around a ' slack-pulley,' shown in 

 the foreground, from which it passes back around 

 one of the guide-pulleys in the street, and back on 

 its way through the tube. The ' slack-pulley ' is 

 m.ounted on a car which is moved by a differential 

 lever in such a manner that the cable is always 

 kept at a uniform tension. Thus the lengthening 

 and shortening of the cable through variations of 

 temperature, etc., is compensated for. 



The grip used for the duplex system, as well as 

 the tube, pulleys, and track-supporting framework, 

 is shown in fig. 9, which is a transverse section of 

 the Tenth Avenue road. The framework and 

 tube used on the Chicago cable-railway is shown 

 in transverse section in fig. 10, which also shows 

 one of the guide-rollers for carrying the cable 

 around a curve. The road-bed of the cable-rail- 

 way in this city has a framework of iron, as 

 shown in fig. 9, concrete forming the sides and 

 bottom of the conduit or tube. The transverse 

 trusses are placed five feet apart, with the slot- 

 rails and track-rails bolted to them. The slot-rails 

 form the sides of the longitudinal slot of the tube, 

 and they are held firmly in place by tie-rods 

 which connect them with the outer edge of the 

 truss. Pulley-vaults are provided at intervals 

 of thirty-five feet, affording access to the carry- 

 ing-pulleys. A system of drainage-pipes con- 

 nects these vaults with the city sewers, thus 

 securing perfect drainage, which cannot be af- 

 fected by any dirt that may accumulate in the 

 conduits. The carrying-pulleys are twenty-two 

 inches in diameter, and are j^laced in pairs, one a 

 little in advance of the other, to support the two 

 cables independently. 



The first cable street-railway, that on Clay 

 Street hill, San Francisco, was looked upon as an 

 experiment to a great extent ; but after a satis- 

 factory trial of three years, the system having 

 proved itself a mechanical and financial success, a 

 second road was constructed, also in San Fi-an- 

 cisco. This was followed by others in rapid suc- 

 cession, until that city has at present upward of 

 twenty miles of cable-road in operation. Other 

 cities followed the lead of San Francisco, St. 

 Louis with sixteen miles, Philadelphia with 

 twelve, Chicago with ten, Kansas City with eight, 

 and many more with shorter lines, so that at pres- 

 ent the total length of double-track cable street- 

 raUway in the United States will not fall far short 

 of one hundred miles. Taking into consideration 

 with this the fact that cable-roads are making 

 rapid headway in Europe, Mexico, Australia, and 

 New Zealand, it will be seen that the new system 

 of street-car traction has proved its right to a 

 prominent position in railroad economics. 



THE PHYSICAL BASIS OF AESTHETICS. 

 Aesthetic impressions may be conveniently 

 divided into two classes : in the first it is the ap- 

 preciation of qualities furnished immediately by 

 sensation that gives rise to beauty, while in the 

 second class the sense-impressions are interpreted 

 and made significant by a guiding thought or emo- 

 tion. Though the two often go together, there is 



