42 Mr Henwood on the Expansive action of Steam 



an image at the bottom of a sort of camera in the " Microgra- 

 filiia" and which, by UEMOViNa the body and eyeglasses, 

 acts like an ordinary solar, and in this state, of course, I call it 

 a " Solar Achromatic Microscope," because its optical part 

 consists of one or more achromatics combined, acting xoithout 

 the aforesaid body and eyeglasses, which would make it mag- 

 nify too much to form an image on the wall of an apartment. 



The following is the version of this affair given by Sir D. 

 Brewster in a note to his account of my " Solar Camera Mi- 

 croscope^' (as he calls it) at p. 115. 



" L)r Goring calls this instrument a Solar Engiscope, while 

 he gives the name of Solar Microscope to the same instrument, 

 when used in a dark room in the common way. The intro- 

 duction of the image into a camera, becomes thus the reason for 

 changing a microscope into an engiscope. The word engiscope, 

 however appropriate it may be, as a companion to the word 

 telescope, is quite inapplicable to any kind of solar micro- 

 scope." 



On the Expansive Action of Steam in some of the Tumping 

 Engines on the Cornish Mines. By William Jory Hen- 

 wood, F. G. S., Secretary of the Royal Geological Society 

 of Cornwall, H. M. Assay-Master of Tin in the Duchy of 

 Cornwall.* 



The experiments which it is my purpose to describe, were 

 instituted with a view to the determination of the quantity of 

 steam employed, and the mode of its distribution on the work- 

 ing-stroke ; the duty performed with a given quantity of fuel ; 

 and the work accomplished for a certain expense. 



I. The quantity of steam employed, and the mode of its dis- 

 tribution on the working-stroke, were approximated to by the 

 use of an indicator, lent me for the purpose by Robert Were 

 Fox, Esq. It consists of a brass cylinder about eleven inches 

 long, and 1.6 in diameter, open at both ends, and accurately 

 fitted with a piston, which, when at rest, is retained near the 

 middle of the cylinder by a spiral spring, of which one end is 



* Slightly abridged from the second volume of the Transactions of the 

 Institution of Civil Engineers, 



