Progress of Invention. 475 



tageously, from that used in this country. The motive power is 

 compressed air, the compression being produced by meMns of the 

 water supply, which, in Paris, is highly effective, the head of water 

 being very considerable. Water being let into one tank, the air 

 expelled from it by the water is transmitted to an air tank, of which 

 there is one at each extremity of the line. Each of the tanks is of 

 iron plate, and holds about one thousand gallons. The time ex- 

 pended in tilling the water tank is about three minutes, and the 

 air thus expelled from it is more than enough to propel the waggon 

 along the entire line, which is about two miles in length. The 

 waggon is of a peculiar form, being a hollow piston about five 

 and a half feet long, closed permanently at one end, and temporarily 

 by a movable lid at the other. Leather washers placed around the 

 closed end, fill up the space between it and the pneumatic tube, 

 which is two and half feet in diameter. The signals between the 

 stations are made by electric bells ; the waggon announces its 

 approach by the noise which it makes. When it is to be sent off, 

 it is placed in the mouth of the tube, which is then put in connec- 

 tion with the compressed air, the other extremity bein^- put in con- 

 nection with the atmosphere, that the air in front of the waggon 

 may have a means of escape. This system is very simple, economic, 

 and effective, but it is applicable only where the head of water is- 

 great. In Paris it is very considerable, and a pressure is therefore 

 produced by it which affords a motive power applicable to a great 

 number of useful purposes. 



Utilization of the Electric Light. — The brilliant light afforded 

 by electricity naturally suggested, at a very early period, its applica- 

 tion to the purposes of illumination. But every project for the 

 purpose was practically impossible, until very great progress had 

 been made in the modes of producing and manipulating that obtained 

 by means of the pile, or the magnet. Galvanic electricity, which in 

 its application preceded that derived from magnetism, appears not 

 unlikely to maintain its ground as a convenient and economic source 

 of light, notwithstanding the numerous and important discoveries 

 that have been made in this department of science. This might 

 fairly be expected : since, at least in those contrivances in which 

 heat and light are the results of the transformation of motion — pre- 

 viously obtained directly from combustion — the effect must be more 

 costly and complicated than when obtained directly from combus- 

 tion, as is the case with galvanic electricity. The effects produced 

 by the latter is now so economic, and what is still more important, 

 so reliable, that it is being introduced with excellent effect in 

 Prance, as a means of diffusing to great distances a light so intense, 

 that when it is used, collision at night is impossible. Al^o, during 

 the intense frosts in, January, the skaters in the Bois de Boulogne 

 were enabled, by means of fifteen electric lights, suitab'y disposed, 

 to enjoy their pastime by night, with at least as much convenience 

 and security as by day. Each of the fifteen lights was product d by 

 the electric current obtained from a Bunsen battery containing 

 forty elements, and placed in a small closed pit, from which the 

 vapours were coriv<- \ , so as to be the cause of no incori- 



