PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION, 505 



apparatus which consisted in the use of a vessel of mercury so 

 placed as to be vaporized, in case the metal was overheated, and 

 by the expansion of its vapor to act on a diaphragm outside. 



In answer to a question of the Chairman ; he thought the 

 heaters would last a long time, but had no means of knowing 

 definitely. Stirling's lasted from two to three years, and he saw 

 no reason why the Wilcox heaters should not last as long. 

 Another difficulty heretofore experienced had been the proper 

 lubrication of the different parts. When kept at a proper tem- 

 perature there is no difficulty. By the circulation of air within 

 the working piston the metallic packing was kept at a sufficiently 

 low temperature. Above the metallic packing Mr. Wilcox places 

 a cotton one, saturated Avith oil which keeps the cylinder prop- 

 erly lubricated. By the use of the economizer the valve is kept 

 at a temperature not over 300", and is therefore easily lubricated. 

 In answer to a question by Mr. Churchill, Mr. Babcock stated that 

 the contents of the economizer was about one-fourth that of the 

 working cylinder. 



The Chairman inquired what the power of the engine was ? 



Mr. Babcock never tested the power of the engine by the brake, 

 but had seen an 18-inch engine performing work which he judged 

 to be equivalent to two horse power. 



A Member. — Do I understand that an engine of two horse 

 power running a day of twelve hours will consume 60 lbs. of coal 

 per day ? 



Mr. Babcock. — If we assume the 18-inch engine to be two horse 

 power then this was the fact, which was equivalent to 2^ lbs. of 

 coal per hour for each horse power. 



Mr. Schuartz inquired what was the difference of action be- 

 tween this engine and the Ericsson, and spoke highly of the in- 

 genuity displayed in the arrangement and operation of the two 

 pistons within one cylinder in the latter. 



Mr. Babcock said he did not wish to detract from the merits of 

 the Ericsson engine, but stated that the peculiar motions required 

 in that arrangement limited the speed to a low figure. By the 

 use of the two cylinders Mr. Wilcox obtained an ease and smooth- 

 ness of motion which enabled his engine to run at a much higher 

 velocity, and in consequence with an increased power. He also 

 avoided the noise and the destructive effect due to such irregular 

 motion as was necessary in the Ericsson engine. Mr. Babcock 

 then explained by means of diagrams the position of the piston 



