1878.] Prof. B. Stewart. Magnetic Declination. 81 



comparison with the Kew standard thermometer No. 515, the property 

 of the Royal Observatory. 



If the readings of the thermometer be corrected for index errors 

 only, as is the case under ordinary circumstances when observations 

 are made, the difference between the Greenwich and Kew standard 

 barometers is reduced by the amount of (0°'5 X 0*0027 =) '0013 inch, 

 and the two barometers differ only by the amount — O'OOOl inch, that 

 is to say they virtually agree. 



In conclusion I would beg to express my thanks to the Astronomer 

 Royal and Messrs. Ellis and Nash for the courteous manner in which 

 they afforded us every facility and assistance in carrying out these 

 comparisons, and to Messrs. Baker, Foster, and Constable for the 

 assistance they have given in the reduction of the observations, as well 

 as in the actual comparisons. 



The tables containing the detailed observations are preserved at the 

 Kew Observatory for reference. 



Note. — Since the effect of the gas burners upon the Greenwich 

 barometer has had attention called to it, Mr. Ellis has fitted opal 

 glass screens between the gas-jets and the barometer. By this means 

 the temperature is rendered much more equable round the instrument. 



II. " On the Diurnal Range of the Magnetic Declination as re- 

 corded at the Trevandrum Observatory." By BALFOUR 

 Stewart, LL.D., F.R.S., Professor of Natural Philosophy 

 at Owens College, Manchester. Received November 28, 

 1877. 



1. The Observatory at Trevandrum was supported by His Highness 

 the Rajah of Travancore, and its Director was Mr. J. A. Broun, F.R.S., 

 who has recently published the first volume of the results of his 

 labours, giving the individual observations of magnetic declination, 

 and deducing from them conclusions of great scientific value. 



Among the other results published by Mr. Broun, are the diurnal 

 ranges of the magnetic declination at Trevandrum, for each civil day 

 in the eleven years, 1854 to 1864. (Table LVIII, page 163.) 



In one respect the treatment of the declination ff nervations at Tre- 

 vandrum differs from that pursued a.t the Kew Obsjj rvatory, inasmuch 

 as in the former place, where disturbances are lit/ ie felt, the diurnal 

 ranges are from all the observations. 



The geographical position of the Trevandrum Observatory was as 

 follows : — 



Latitude, 8° 30' 32" N. 



Longitude, 5h. 7m. 59s'. E. of Greenwich. 



A. Annual Variation of Declination-Range. 



2. The following table exhibits mean monthly results of the decli- 

 vol. xxvn. a 



