C >44 3 
XIV. On the derangements of certain transit instruments by the 
effects of temperature. By Robert Woodhouse, A. M. 
F. R. S. &c. 
Read April 26, 1827. 
In the Philosophical Transactions for 1825, Part II. p. 418, 
I gave an account of the transit instrument belonging to the 
Observatory at Cambridge. Amongst other circumstances, 
I mentioned one of a derangement of the telescope arising 
from an unequal expansion of its braces, I established, as I 
thought, by direct .experiments, the existence of such a 
derangement, and pointed out /its cause. In a subsequent 
volume of the Transactions (1826, Part II. p. 75), I gave an 
instance of the quantity of such derangement caused by the 
sun's rays falling on the upper western brace. That circum¬ 
stance caused a retardation of 20 seconds in the passage of 
Polaris at its lower culmination. 
The removal of the braces, which, after the above experi¬ 
ments I judged to be a necessary measure, has, from one 
cause or another, been delayed till this time. I have how¬ 
ever derived some good from my procrastination, since it 
has enabled me to institute the experiments which I am now 
about to detail. 
These experiments have been made in consequence of some 
observations lately presented to the Royal Society, a copy of 
which Mr. South, their author, has been kind enough to send 
me. The results which Mr. South has drawn from these 
observations, in what regards the effect of the braces of his 
