XXX 



(/°-26°) 

 k 



Inteoduction. 



(q + 2e-e\ 



q + 2e - e'\ +3000 



The adopted value of ^ = 0-000294. See § G. 



6=0000103 e'= 0000106. 



Table 11. — ^Values oi k and q for the Bifilar Magnetometer, and the periods to 



which tliey apply. 



Pericds to which the Values apply. 



Value of k. 



Value of q. 



1841. 







d. 1i. rt. h. 





Sc. Div. 



July 11 20- -July 23 5 



0001185 



2-57 



Aug. 4 20 - Sept. 7 5 



00001522 



200 



Se t. 7 20 - Sept. .30 5 



0001464 



208 



Oct. 6 20--Oct. 19 20 



00001.303 



2-34 



Oct. 19 23— Dec. 31 5) 



0-0001248 



2-44 



and during 1842 j 







A m 



33. As I have had much doubt of the exactness of the values of , I have 



m 



in all cases given the temperatures along with the corrected observations, so that 

 each magnetician may have it in his power to apply a more accurate correction, if 

 such is to be found. 



A Tfh 



It is obvious that, supposing the value of to be well determined, the accu- 

 racy of the corrections will depend on the temperature of the magnet being well 

 ascertained. 



The error in the observations of the scale will be generally less than 0"1 scale- 

 division ; the error in reading the thermometer may be O"*! Falir. ; the consequent 

 error in correction may, therel'ore, be upwards of 0*2 scale-division. 



The thermometer, by Ross, has a bulb 0*5 inch in diameter ; it is inclosed in a 

 glass tube, open at the bulb, which fits into the lid of the magnetometer-box, leav- 

 ing the stem and scale above, and the bulb below. The box, like that of the Declino- 

 meter, was not well closed, and it was soon evident that during a rapid rise or fall of 

 temperature, the thermometer would indicate more or less than the temperature of 

 the magnet. 



The fire lighted in the morning, during the winter months, conspired with the 

 temperature of the day to make the increase more rapid than it would otherwise 

 have been ; and there is little doubt that the indications of the thermometer would 

 frequently exceed the temperature of the magnet by 1°*0 Fahr. 



In 1843, having formed inner boxes, and had the whole well closed, Messrs 



