502 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



Mr. Garvey stated that there was a maximum and a minimum 

 pressure. 



Adjourned to Wednesday evening, October 31st, 1860. 



American Institute, Polytechnic Association, ) 

 October 31, 1860. ) 



Prof. Mason in the chair. 



The Chairman proposed three questions to be answered by 

 those explaining the engine. First, as to the burning of the 

 heaters ; for if they are liable to be burned out frequently, it is 

 an objection to its economical use, not only from the expense, 

 but from the frequent interruptions in the working of the engine. 

 The second, also in the form of an objection, relates to the small 

 amount of force that could be accumulated. The air being 

 heated as it is used, no provision can be made, as in the steam 

 boiler, for a supply of work for a little time. The heating up 

 occurs at the moment, and is liable to disappointment, upon the 

 slightest accident or occasion of delay. The third and strongest 

 objection relates to the small amount of power that is obtained. 

 It is only changing one gas, not into another, but an expansion 

 of the same gas ; whereas, in making steam, we expand a liquid 

 instantly to 1700 times its bulk. In air engines double the 

 volume is all that is usually obtained. He would like to hear 

 either some one answer to these objections, or evidence that in 

 spite of these objections, the economy is such as to make the 

 caloric engine valuable. 



CALORIC engine. 



G. H. Babcock. — Although the science of air is comparatively 

 in its infancy, yet it was not so recent or so unexplored as many 

 might suppose. Down to the present week there have been 

 issued in this country thirty-five patents for air engines and 

 improvements therein. In Great Britain the number is much 

 larger, the official list showing upwards of 200 patents for the 

 same object. All these inventions may be classified in four 

 grand division of classes. Bach class may be capable of sub- 

 division. The first class may include those engines in which a 

 reservoir of compressed air is used, similar in its effect to a 

 steam boiler. 



Second class are those which use the gaseous products of com- 

 bustion ; it also includes the explosive ones. 



Third class. This class would include those engines which 



