i:75D 



VII. On the transit instrument of the Cambridge Observatory ; 

 being a Supplement to a former Paper. By Robert Wood- 

 house, Esq. Plumian Prof essor of Astronomy in the University 

 of Cambridge. 



Read January 19, 1826. 



Jln 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 : 



