C 75 ] 
VII. On the transit instrument of the Cambridge Observatory ; 
being a Supplement to a former Paper. By Robert Wood- 
house, Esq. Plumian Professor of Astronomy in the University 
of Cambridge. 
Read January 19, 1826. 
In the brief account of the transit instrument which I had 
the honour some time ago of presenting to the Royal 
Society, I stated the circumstance of the instrument's devia- 
tion from the meridian arising from the unequal expansion of 
its braces ; but no instance was then given of the magnitude 
of such deviation. I now subjoin one. 
On the morning of Oct. 15, (civil reckoning) after ob- 
serving the passage of Regulus, the southern shutters were 
accidentally left open, so that when I returned to observe 
the inferior culmination of the pole star, the sun was shining 
on the upper western brace, the object-glass of the instrument 
being towards the zenith. The effect of this was a retarda- 
tion of more than 25 seconds in the star’s passage, as will 
thus appear : 
Oct. 14. j 
O h 59® 20 s 
Polaris. 
Rate of Clock 
> 
12 59 44 
Polaris S. P. 
— .17 
Oct 1 5 - | 
0 59 20 
12 59 17 
Polaris. 
Polaris S. P. 
Reversed the 
> 
Oct. 16. 
0 59 19.5 
Polaris. 
axis. 
Oct. 17. 
&c. 
0 59 20 
Polaris. 
