1865.] Mr. Gassiot Description of a Rigid Spectroscope. 325 



TABLE II. 



Temp. Temp. Difference 



Date. Air. Prism. Eeadings. for 20. 



February 16 48'5 42 -5 4-60] 



.... 58-0 52-5 5-09 I = 0-96 



69-5 62-5 5-56 J 



17 50-0 42-5 4- ] 



57-5 52-5 5-08 I = 0'92 



67-5 62-5 5-54 j 



18 48-0 42-5 4-60 



Variation of temperature correction for a change of temperature 

 of 20 0-0004 inch. 



TABLE III. 



Having thus far satisfied ourselves by observing under varied tempera- 

 tures, and also that the removal of the instrument to different parts of 

 Mr. Browning's premises did not affect the readings on the 22nd of March, 

 the apparatus was removed in a cart to Kew Observatory, and placed in 

 one of the rooms for observing, when the following readings were made : 



Temp. Temp. 



Date. Air. Prisms. Beading. 



March 23 45'0 42'2 4'57 



Mean of readings taken in the Minories, at a temperature of 42 0> 5, 

 4'60 ; change of zero during the transit, 0'0003 of an inch. 



Observations were subsequently continued under the direction of Mr. 

 Stewart. 



