4^4 Major- General Roy's Account oj the 



the other three to the braces which run acrofs it. This cop- 

 per trough has llkewife a cock in the left-hand end ; and m 

 the general plan a caft iron prifni is reprefented in it ; but this 

 lafl: carries no apparatus, as thofe in the wooden troughs do, 

 being exa6lly of the length of five feet, and only placed there 

 as one of the rods whofe expanfion was tried, and to fliew that 

 the machine v/as capable of receiving a rod of that weight 

 and magnitude. 



By referring to the general plan It will be feen, that twelve- 

 lamps are made ufe of to bring the water in t^ii^ copper to boiL 

 They ftand on four fhelves, three in each compartment formed 

 by th^e crofs braces of the frame. They can readily be pufhed 

 forwards or drawn backwards, and when a6lually in ufe, their 

 handles are only feen, projedling from under the copper. It 

 was found, by burning oil in the lamps, the heat of the water 

 could not be raifed above 209"" or 210"^? but with fpirits of 

 wine it was brought into violent ebullition. The plan of the 

 frame llkewife fhews, that the tubes of the microfcopes are 

 fub-divided into feveral diflincfl parts ; and that one of thefe 

 parts is attached by a collar to a mahogany prifm, which reaches 

 from one end to the other. But the ufe of thefe contrivances 

 it will be beft to defer fpeaklng of, till after having defcribed.; 

 the apparatufes that are placed within the copper boiler. 



At the bottom of the plate the boiler is reprefented, both in 

 plan and longitudinal fe£lion, to a fcale of one-fourth part of 

 its real dim.enfions. It contains within it two brafs Aides, the 

 one long and the other fhort ; which, from the braces that 

 bind the cheeks together, very much refemble the form of a 

 ladder. The long Aide, whofe cheeks are i| inch deep, 

 reaches almoft the whole length of the copper, although every 

 where unconneded with it except at the points A and B. At 

 I the 



