44$' Major-General Roy’s Account of the 
ftrengthen the cafes., but more particularly to prevent them 
from being rent when long expofed to the fun’s rays in the 
field, the (ides are covered with brown linen laid' on very 
imoothly, and carefully glued with thin glue, ufed as a flronger 
kind .of pafte, to which, it may. yet.be neceffary to add a coat 
of oil paint. 
Each of the glafs rods, completed ; in the manner above- 
mentioned, weighs about fixty-one pounds.. Their lengths 
were afcertained by means of new brafs points placed in the 
great plank, the fpaces of forty inches being laid off, with the 
ntmofc care, from the brafs fcale, when the temperature of all 
bad remained for the greater part of two days (AuguR 15th 
and 1 6th) at or very near 68°. For this purpofe two brafs 
reffangular cocks, whofe alternate furfaces had been previoufly 
ground together, were placed upon the plank, fo as to bifedh 
the extreme dots.; in which fituation they prefented to each 
other furfaces that were truly parallel. The rods being then feve- 
xally placed between the cocks * (or, .as. was found to be a. better 
method* 
* The firft of thefe cocks, or that to which the fixed button was applied, had 
a hole in it exactly of the, height of the, center of the button, and large enough 
to permit the point of the, micrometer fcrew tOfpafs, through it, the faid fcrew: 
being fixed on .the farther iide, or beyond the cock. . Thus, while the tempera- 
ture continued .accurately at . 68°, the fixed button, or any other plane furface, 
being brought up to the hole in the cock, - and' the micrometer point fcrewed fo 
far as juft to touch it, the coincidence continuing in the interim perfect, the exa& 
diftance of tw r enty feet was obtained between the point ,of the fcrew and the 
fepond cock ; at which time the divifion anfwer.ing to the. index on the head of the 
micrometer ,wa,s carefully noted. , This being done, the cock with the hole was 
removed from the plank, and the rods were feverally adjufted by being placed 
between the point of the fcrew and the fecond cock. This Tubftitution of the 
micrometer point, inftead of the firft dock, was found neceffary j becaufe, during 
the operation of adjuftiuent, the temperature . would fometimes change a degree, 
generally 
