130 On the instantaneous Production of Fke 



will appear as distinct when seen together, through thl* 

 small aperture, as when they are viewed separately by the 

 naked eye. 



Experiment W. — A piece of wire being placed in a line 

 between a remote object and my eye, at the distance of two 

 feet from it, these two objects appeared more distinct when 

 seen together through an aperture of -^ of an inch in di- 

 ameter, than when they were viewed separately by the na- 

 ked eye. 



It is evident that no change took place in the humours af 

 the eye, in these experiments, neither in the convexity of 

 the crystalline lens, nor in its distance from the retina; con- 

 sequently that hypothesis which is built upon a supposition 

 that the crystalline approaches to, or recedes from, the re- 

 tina, by the contraction and dilatation of the ciliary pro- 

 cesses, must be erroneous. For it is absurd to suppose that 

 the crystalline lens can be at different distances from the re- 

 tina at the same time ; and it is equally as absurd to assert, 

 that the crystalline lens can, at the same lime, have diffe- 

 rent degrees of convexity. 



I am, sir, your obedient servant, 



Lynn. Ez. Walker. 



June 17, 1808. 



XXV. On the instantaneous Production of Fire, hy the mere 

 Compression of Atmospheric Air. By Freuekick Ac- 

 CUM, M.R.I. A., Operative Chemist, Lecturer on Prac- 

 tical Chemistry and on Mineralogy and Pharmacy, ^c. 



In the xivth volume of the Philosophical Magazine, p. 363, 

 professor Pictet communicates the accension of combustible 

 substances by the rapid compression of atmospheric air. 

 The discovery of this curious fact is doe to Mollet, as ap- 

 pears from the Journal de Physique for Messidor, An. XI f. 

 It is there slated, that if the air be very suddenly compressed 

 in the ball of an air-gun, the quantity of caloric liberated 

 by the first stroke of the piston is sufficient to set fire to a 



piece 



