492 Mr. T. Gray on Measurements of the Intensity of the 



The magnets were found to change by gTooo" °^ ^ e * r Y ^ ue 

 per degree centigrade change of temperature ; but as the change 

 of temperature never exceeded two or three degrees, this cor- 

 rection was neglected. 



The correction for induction, however, was found to be 

 considerable in some cases, and the results tabulated below 

 have all been corrected for that. 



The Temperatuee Coefficient was obtained by placing the 

 deflector behind the magnetometer-needle in such a position 

 as to produce a deflection of 1000 scale-divisions, and the 

 change of deflection produced by raising the temperature 

 about 40° C. observed* 



The Induction Coefficient was determined by placing the 

 deflector, surrounded by a magnetizing coil, near the magneto- 

 meter-needle, and observing the change of deflection produced 

 by passing a known current through the coil. The arrange- 

 ment for these measurements is illustrated in PL XI. fig. 3 ; 

 and the results of a number of experiments on the effect of the 

 length and hardness of the deflector on this correction are 

 given in Table II., and are shown diagrammatically in the 

 following curve. 



Curve illustrating the effect of Batio of Length to Diameter on the 

 Inductive Coefficient. 



1 



■g -80 





















S3 

 >> 



2 

 & -6o 







































c 



•> 



g 



o 



e ■«» 



"S 



|-40 



E 



o 



& *30 



i 



u 



V .on 











































































fee 20 

 9 



C 

 6 



u 





















i 3 'io 



Oh 





















40 50 eo 70 80 90 



Ratio of length to diameter. 



