experiments made with an invariable pendulum. 9 
instrument in a satisfactory manner, being perfectly steady 
and distinct. 
The allowance made for expansion, not being the result ol 
experiments actually made on this particular pendulum, but 
from the deductions resulting from Captain Kater’s experi- 
ments on a bar exactly similar, it became important in order 
to render the experiment strictly comparable with that at 
Greenwich, to keep the temperature of the room as near as 
possible to the one in which the previous experiments had 
been performed in England, namely, 50°. From the small- 
ness of the room it was soon found, that the stove placed 
within it, produced incessant fluctuations in the temperature ; 
it was therefore removed outside, to about six feet from the 
north wall of the house, and sunk into the ground level with 
the foundation of the observatory ; built round with stones, 
and a tent was pitched over it. The room was now warmed 
by the smoke-pipe passing through it ; and, to preserve the 
temperature of the pendulum more uniform, a large triangular 
covering of fearnought lined with racoon skins, was made to 
enclose the whole apparatus, except that part of the front 
required for observation. These arrangements effected the 
object so far, that the temperature of the room was seldom 
more than 3 0 , and frequently not one from 50° during the 
observations. By a Sixes’ self-registering thermometer, the 
mean range of temperature to which the pendulum was ex- 
posed in 24 hours was only 8°, and the extreme not more 
than 12 0 during the series in June, whilst that of the atmo- 
sphere, varied from 23 0 to 47° of Fah. without any uniformity. 
Under these circumstances the pendulum of experiment 
was placed in theY’s on the 29th of May, 1825, and the 
MDCCCXXVI. * C 
