25^ , DISEASES OF WHEAT., 



alternately above and below the piston of the cylinder A. 

 In f ach pipe is fixed a stop cock or valve, so constructed as 

 to open a passage to the external air, when it shuts the con- 

 nexion with the fire vessel. These cocks are worked by a 

 plug frame. 



From this construction it will appear evident, that what- 

 ever expansion the air receives, its pressure will operate alike 

 upon the piston of the bellows and of the receiver; and 

 that always in opposition to each other : Hence the power of 

 the stroke will be in proportion to the excess of the area of 

 the receiving piston, over that of the feeding one, multiphed 

 by the expansive force of the contained air, and by the 

 length of the movement. 

 The engine If, when the engine is well constructed, the expansion of 



maybe usRd for ^},p ^j,. \^ keeping up the fire be not found sufficiently sensi- 

 p^ed water. b^^> ^^'^^ *^^ form of the engine is such as to admit of either 

 inflammable gas, oil of tar, or other inflammable matters, 

 being injected, each stroke, upon the fire; so that all the 

 heat generated by the united combustion may operate 

 without waste ; perhaps even a slight sprinkling of water, 

 either upon, or round the sides of the fire, might answer the 

 purpose. It scarcely need be observed, that a tube con- 

 nected with a small forcing pump are the only things re?- 

 c^uired for producing these effects. 



I remain, Sir, 



Your obedient Servant, 



GEORGE CAYLEY, 



A Letter from Mr. Rob«rt Harrup to the Editor, on ike 

 Diseases of Wheat, 



To Mr. NICHOLSON. 

 SIR, 



Keference to JLn a former communication on smut in wheat, inserted ia 



the author's you|. Journal last year, I gave an account of some experi- 

 former paper. ■^ , , , . . , i. i i- 



inents which proved, that the principal cause oi the disease 



