Mechankai Science. 347 



of its length, and passing off gradually into the general surface 

 of the plug, so as to form a kind of inclined plane on it. This 

 groove extends half way round, and is so arranged that 

 when the plug is put into its place, it shall receive the end 

 of the valve c, the length of the valve, and the depth of the 

 groove being such that the former may perfectly enter into and 

 close the conical aperture e, when its extremity c is in the 

 middle of the groove. Now, it is evident, that whilst the cock 

 remains in this state, it is shut against the passage of any gas 

 through it, not only by the conical valve, but also by the dis- 

 union of the two grooves; when, however, the plug is turned, 

 the plane, which the groove in it forms, presses on the end of the 

 valve, and opens it either more or less, according as it is more 

 or less turned round, and, at the same time, the end of the plug 

 groove passing over the end of that in the box, opens a channel, 

 by which the gas passes off, which has already made its 

 way by the valve. The emission of the gas may, in this way, 

 be regulated with great nicety, and its retention, if required, 

 secured in a very perfect manner. The plug is retained in its 

 place by the screw Z, or, as in the usual manner ; and, it is 

 evident, that the end e of the stop-cock is that which is to be 

 inserted into the vessel intended to contain the gas. Sig. 

 Crivelli has particularly applied these stop-cocks to the con- 

 densed air blow-pipe. — Giornale di Fisica. T. 2., p. 92. 



4. Substitute for a Copying Machine. — Write with common 

 writing ink, in which lump sugar has been dissolved, in the 

 proportion of four scruples or a drachm and a half of sugar to 

 an ounce of ink. 



Moisten copying paper, (a paper which is sold at the sta- 

 tioners at Is. lOrf. a quire for the Copying Machines,) by 

 passing a wet soft brush over it ; then press it gently between 

 soft cap paper, so as to smoothen it and absorb the superabun- 

 dant moisture. 



Put the paper so moistened upon the writing, and both be- 

 tween cap or other smooth soft paper, placing the whole on the 

 carpet or hearth-rug, one end of which is to be folded over it. 



