Gleanings from the International Exhibition. 143 



operative chemists, who not unfreqnently desire to draw a cur- 

 rent of air or gas through a tube. For this purpose, however, a 

 far superior instrument has been for some time in use in France ; 

 and as it appears to be quite unknown in this country, we have 

 much pleasure in describing its structure and mode of action ; 

 its great advantage being that it is capable of beiug continued 

 in operation during a very great length of time with the same 

 supply of water. It consists of two reservoirs placed one above 

 the other, and which are capable of being turned easily on the 

 horizontal axis b f, which supports them. In the position 

 shown in the figure the air is drawn in or aspired through the 

 flexible tube ending at b, and is conveyed above the level of 

 the water at c, into the upper vessel, replacing that which falls 

 into the lower reservoir by the canal d d. The air in the lower 

 vessel escapes by the tube e p as the water enters. 



When all the liquid has fallen out of the upper reservoir 

 it is evident that the action of the instrument ceases ; but it 

 is capable of being immediately renewed by simply turning 

 the two reservoirs so as to bring the one filled with water 

 uppermost, when, as they are constructed in a manner precisehy 

 identical, the liquid will again flow, and the aspiration of air 

 proceed until the water has again flowed into the lower vessel, 

 which may be then returned to its original position, and so on, 

 the action continued indefinitely. 



Tb,e engraving is taken from Jamin's Cours cle Physique 

 de VPJcole Poly technique a work which, we may remark, in 

 passing, is far superior to any class text-book of physics in our 

 own language, and which ought to have been translated long 

 since. In this cut the aspirator is represented as drawing air 

 through two U tubes filled with pumice saturated with sulphuric 

 acid, the object being to determine the amount of hydrometric 

 moisture it contains. 



GLEANINGS FROM THE INTERNATIONAL EXHIBITION. 



Microscopic Diamond Writing. — Within the last few days Mr. 

 Webb has placed his apparatus for executing microscopic writing on 

 glass amongst the philosophical instruments in the northern gallery. 

 The instrument may be described as a long perpendicular rod or 

 lever carrying at its lower end a pencil, which is traced over the 

 original writing that is to be reproduced in miniature. The short arm 

 of this lever is concealed in a box above, and acts upon a second lever, 

 the arrangement being repeated until the motion, which originates 

 with the hand below, is reproduced in the required degree of mi- 

 nuteness. 



The extremity of the lever moving through this small space, 



