442 Major-General Royff Account of the 
reflectively. Thus, the. depth of the (ides in one fenfe, and 
the fpring which they have by bending in the other, aft as 
t ruffes, prevent the cafe from warping, and render it fuffi- 
ciently ftrong, although at the fame time, confidering its great 
length, very light. 
The plan of the middle rod reprefents the cafe with the top 
off, that the tube may be feen placed therein : the right and 
left-hand rods have the tops on, whereby may be feen the 
oval opening in the middle of each, fhut by a mahogany- lid ; 
and alfo the pofitions of the two thermometers, with tubes 
bent at right-angles, fo as to place the ball about two inches 
downwards within the cafe, for the better afcertaining the 
temperature of the glafs, as will eafily be conceived, by confi- 
dering the reprefentation of the tube and ball in die feffion 
acrofs the middle of the rod. 
It is to be obferved, that the middle of the tube is made faff 
to the middle of the cafe in the following manner. Firff, 
around the middle of the tube, a quantity of pack-thread, im- 
xnerfed in liquid glue, was wound by feveral returns on itfelf, 
for the fpace of about two inches in length ; and upon this 
mafs of pack-thread, while the glue was warm, a ffrong ma- 
hogany collar was forced ; whereby the three fubftances became 
fo perfe&ly united to each other, that they might be confidered 
as one only. Acrofs the bottom of the cafe in the infide, 
three mahogany braces or girders, one in the middle, and one 
half-way between it and each end, are faffened, by means of 
fcrews, to the bottom and fides. Thefe rife about if inch 
above the bottom, fo as to place the axis of the tube, when in 
ufe, about 2f inches above the furface of the ffands on which 
it reffs. The end- pieces of the cafe are likewife of mahogany * 
about i % inch thick. Each confiff s of two parts 3 a lower and an 
upper. 
