Profrbsor Thomson's Notice of Stirling's Air Engine. 109 



cotton, and I had no reason to suppose the last portion perfect, considering 

 the difficulty with which some of the previous stages of improvement had 

 been attained. 



The specimen I have thus examined consists, therefore, of — 



96-59 gun-cotton (12 C, 7 H, 7 0, 3 NO,.) 

 3-41 lignin (12 C, 10 H, 10 0.) 



100-00 



And pure gun-cotton consists of — 



24-24 = 12 C. 24-24 = 12 0. 



21-21= 7 HO. 2-36= 7 H. 



54-55= 3 NO,. 1414= 3N. 



59-26 = 22 0. 



100-00 



100-00 



It is lignin in which three atoms of water are replaced by three atoms of 

 nitric acid. 



21s* April, 1847. — The Vice-President in the Chair. 



On the motion of Mr. Liddell, the Society agreed to request Dr. R. D. 

 Thomson to undertake the duties of interim Librarian, in room of Mr. J. 

 J. Griffin, who resigns in consequence of his being about to remove to 

 London. 



XXVIII. — Notice of Stirling's A ir Engine. By William Thomson, B. A., 

 Professor of Natural Philosophy in the University of Glasgow. 



Professor William Thomson gave an account of Stirling's Air Engine, 

 and exhibited a working model. 



Attention was called to the circumstance that, in accordance with 

 Carnot's theory,* of which an explanation had been given by Professor 

 Gordon at a previous meeting of the Society, the mechanical effect to be 

 obtained by an Air Engine, from the transmission of a given quantity of 

 heat depends on the difference between the temperatures of the air in the 

 cold space above and the heated space below the plunger; as this difference 

 is considerably greater than that which exists between the boiler and the 

 condenser in the best condensing Steam Engines, it appears that, if the 

 practical difficulty in the construction of an efficient Air Engine can ever 

 be removed to nearly the same extent as already has been done in the 

 case of the Steam Engine, a much greater amount of mechanical effect 

 would be obtained by the consumption of a given quantity of fuel. 



* An account of this theory is given in a paper by Clapeyron on the Motive Power of 

 Heat, of which a translation is published in Taylor's Scientific Memoirs, vol. i. 



