MECHANICS AND USEFUL ARTS. 65 



results may illustrate the use of this method of research. The most con- 

 venient way of expressing the density of steam is by stating the number of 

 volumes into which the water of which it is composed has expanded. Thus, 

 one cubic inch of water expands into one thousand six hundred and seventy 

 cubic inches of steam at two hundred and twelve degrees Fahrenheit; into 

 eighteen hundred and eighty-two cubic inches at two hundred and fifty-one de- 

 grees, and into four thousand cubic inchcs^R: three hundred and four degrees, 

 and so on. In this way, the following numbers have been computed : 



Volume of steam. 

 Temperature. By formula. By experiment. 



244 .... 1,005 896 



245 . . . . .939 890 



257 . . . .790 651 



22 ... .740 680 



268 .... 680 G33 



270 660 604 



283 . . . .240 490 



These determinations, at pressures varying from ten pounds to fifty pounds 

 above the atmosphere, are not accurate reductions from the experimental re- 

 sults, but only approximations. But they uniformly show a decided deviation 

 from the law for perfect gases, and in the direction anticipated by Professor 

 Thomson, the density being uniformly greater than that indicated by the 

 formula. I hope, by the time of the next meeting of the association, with 

 the assistance of my friend Mr. Tate, to be enabled to lay before the section 

 a series of results which will fully determine the value of superheated steam, 

 and its density and volume compared with pressure at all pressures, varying 

 from that of the atmosphere to five hundred pounds on the square inch. 



THE ATMOSPHERIC TELEGRAPH. 



The Atmospheric Telegraph, or device for transmiting small packages 

 through air-tight tubes by atmospheric pressure, which was attempted to be 

 introduced in this country some years since by Mr. Richardson, of Boston, 

 has been recently put into practical operation by the International Telegraph 

 Company of London. Their chief office in that city has been for some 

 time in working communication not only with the Stock Exchange, but 

 also with all the subordinate telegraph stations in the outskirts of London, 

 and written messages .arc constantly transmitted through the tubes thus 

 avoiding the necessity of repeating each message. " We witnessed," says 

 the London Times, " the apparatus doing its ordinary work the other day 

 in the large telegraphic apartment of the company in Moorgate Street. 

 Five metal tubes, of from two to three inches in diameter, are seen trained 

 against the wall, and coming to an abrupt termination opposite the seat of 

 the attendant who ministers to them. In connection with their butt-ends 

 other smaller pipes are soldered on at right angles; these lead down to an 

 air-pump below, worked by a small steam-engine. There is another air- 

 pump and engine, of course, at the other end of the pipe, and thus suction 

 is established to and fro through the whole length. Whilst we are looking 

 at the largest pipe we hear a whistle; this is to give notice that a despatch 

 is about to be put into the tube at Mincing Lane, two-thirds of a mile dis- 

 tant. It will be necessary, therefore, to exhaust the air between the end we 



G* 



