Major-General Roy's Account of the 
the other three to the braces which run acrofs it. This cop- 1 
per trough has likewife a cock in the left-hand end ; and ire 
the general plan a calf iron prifm is reprefented in k ; but this- 
laid carries no apparatus, as thofe in the wooden troughs do, 
being exactly of the length of five feet, and only placed there 
as one of the rods whofe expansion was tried, and to fhewthat 
the machine was 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 the copper to boih 
They {land on four fhelves, three in each compartment formed 
by the crofs braces of the frame. They can readily be pufhed 
forwards or drawn backwards, and when actually in ufe, their 
handles are only feen, projecting from under the copper. It 
was found, by burning oil in the lamps, the heat of the water 
could not be railed above 209° or 210°; but with fpirits of 
wine it was brought into violent ebullition. The plan of the 
frame likewife Aiews, that the tubes of the microfcopes ares 
fub-divided into feveral diffcinft 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 fpeaking 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 hi 
plan and longitudinal feftion, to a fcale of one-fourth part of 
its real dimenAons. It contains within it two brafs Aides, the 
one long and the other (hort ; which, from the braces that 
bind the cheeks together, very much refemble the form of a 
ladder. The long Aide, whofe cheeks are if inch deep, 
reaches almoft the whole length of the copper, although every 
where unconnected with it except at the points A and B. At 
3 the 
