1826.] 



Scientific Notices-^Miscellaneous, 



163 



Elaster or clay), previously mixed with a sufficiency of water, 

 alf a line in thickness. In about half an hour it assumes the 

 consistency of paste, and is then put into the frames over the 

 type, composed in the ordinary way, but not inked ; in this way 

 the printing is modelled, or engraved, in the paste above. These 

 sheets are then dried on a stone plate, and the fused stereotype 

 metal poured over them. The writing will then be obtained in 

 relief on a thin plate of metal, the characters being equally well 

 formed with the original type. The proofs taken from these 

 stereotype plates do not differ from those taken from the form 

 of moveable characters. The author of the discovery proposes 

 to reveal his process minutely, so soon as he has obtained thirty 

 subscribers at 100 florins each. The expence of the apparatus 

 required for making the castings he estimates at 100 florins, or 

 about 11/. 35. Sd., and that of the paper covered with the earthy 

 paste at six kreutzers, or 2.68 pence per sheet. — (Journal of 

 Science.) 



7. On an Air-Pump, without Artificial Valves, By W. Ritchie, 

 AM. Rector of Tain Academy. 



In the common construction of the air-pump the valves 

 are very liable to be deranged, the repairing of which is 

 attended with much trouble and expence. In the following con- 

 struction no such derangement can possibly take place, which 

 must, of itself give this air-pump a decided advantage. 



The machine consists of a barrel 

 shut at the lower end, and having a 

 small aperture at C, forming a free 

 communication with the receiver F; 

 the piston D is solid, and stuifed in 

 the usual way. The piston rod 

 works in a small stuffing box at A, 

 so as to render it completely air- 

 tight. There is a small aperture at 

 E in the top of the barrel, to allow 

 the air to make its escape when the 

 piston is raised. This air-pump may 

 be worked in the usual way, or by 

 the method of continued motion. 

 In commencing the exhaustion of 

 the receiver, the piston is supposed 

 to be below the small aperture at C. 

 The piston is then raised, and the air which occupied the barrel 

 is forced out through the aperture at E. The point of one of 

 the fingers is applied to the perforation, in the same manner as 

 in playing the German flute. The air easily passes by the 

 finger, which, when the piston begins to descend, shuts the 

 opening, and completely prevents the entrance of the external 



