56 ANNUAL OF SCIENTIFIC DISCOVERY. 



similar circumstances. The vacuum was now lowered until the barom- 

 eter gauge showed two inches of water only, and a living passenger, 

 in the shape of a not very handsome dog, was placed, with one ton 

 weight of dead stock, in a carriage. The signal was made by the 

 workmen at the open end of the tube, the communicating valve was 

 opened, and in one minute and a hah the carriage and its four- 

 legged guard were in the engine house, the latter apparently not at 

 alt the worse for the exhausting process to which he had been sub- 

 jected. 



Subsequently two gentlemen were sent through the tube with 

 equal success and celerity. They lay in one of the carriages, on 

 their backs, on mattresses, and reported themselves as experiencing 

 no inconvenience. 



The speed with heavy loads thus far obtained is only about twenty- 

 five miles an hour ; but as this includes the starting and stopping in 

 the short space of a quarter of a mile, the company anticipate a 

 speed ultimately of thirty or forty miles an hour. By forcing air into 

 one end of the tube and drawing it out at the other this speed may be 

 multiplied several fold. 



It is the intention of the company, now that they have obtained 

 parliamentary powers for opening the streets to lay down their 

 tubes, to establish a line between St. Martin's-le-Grand and one of 

 the district post-offices, and ultimately to extend their system through- 

 out the metropolis, so as to connect the railway stations and public 

 offices. 



NEW MODE OF PEESEEVING IMPEESSIONS IN SAND, ETC. 



The murder of an eminent banker on a French railway has given 

 rise to a very ingenious plan of rendering permanent marks in sand 

 or any other yielding soil, and which may possibly be found useful in 

 many cases where it is desirable to preserve an impression that would 

 otherwise be soon obliterated. The process is the invention of M. 

 Hugoulin ; and the manner in which it has been applied, to preserve 

 the marks made by the criminal's feet in the sanely ground of the 

 station where he leaped from the train, is as follows : A sheet of thin 

 iron plate was placed over the marks made, and supported by an iron 

 stand at a distance of about an inch and a half from the surface of the 

 ground ; a quantity of lighted charcoal was then placed on the iron 

 plate, which soon became red hot, and of course heated the spot over 

 which it was placed. "When the latter was raised to 100 Centigrade 

 (212 Fah.), the fire, together with the plate, was removed, and a 

 quantity of finely divided stearic acid was strewed over the impres- 

 sion by means of a sieve. The powder used was that of a common 

 stearine candle, dissolved by heat in alcohol, and then thrown into a 

 large quantity of cold water, when the stearine falls to the bottom in 

 the form of a fine precipitate. This powder is so light and impal- 

 pable, that it is said it might be sifted over an impression in the dust of 

 a common road, without in the slightest degree interfering with the 

 faintest mark. The instant it touched the heated surface of the 

 ground in question, it melted, and, as it were, sealed the whole of 

 the loose atoms into one compact mass. When a sufficient quantity 



