T>64 



Mr. M. Solomon on tin 



x /?o 



/6o 



the change being slightly more marked at the short periods. 

 (See Table III. and fig. 3.) 



Table III. — Rosenthal Galvanometer. 



Pe s "conds m !" 386 4 ' 33 5 ' 61 6 ' 7 ° 81 ° 9 ' 25 10 ' 4 ° ll '° 8 12 ' 80 15 ' 8 ° 18 ' 6 ° 



temaU) ' 0228 °* 0256 C " 0330 °" 0382 °" 0459 °' 0523 °" 0597 °' 0618 ° 0709 °" 0873 °" 113 

 Ration/A 169-5 1693 170 175 176 177 175 179 180-5 181 182'5 



Fio". 3. 



: z " "EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEJEJEEEEEEEEEEEEl 



' -r ~— ' ~ 



EE|EEEEEEEElEEEEEEEEEEEEEEEEEEEEE|EEEE-E|E,E|i^iEEEE 



:::::::::::::::x:ii::H::: = :::::::::::::::::::::::: = iT ====:===I==:== 



7* 



Period, t, 



to 



in Seconds. 



/2 6' 



These experiments (which have been selected from amongst 

 the large number made at the Central Technical College as 

 being typical) succeed in establishing the fact that the ratio 

 tj\ does not remain constant when the strength of the con- 

 trolling field is altered, but they do not explain why the 

 r.onclusion derived from the theoretical equation is not borne 

 out in practice. At the suggestion of Mr. Mather I made 

 a series of experiments to find out if possible to what cause 

 the variation in the ratio was due. It has been shown above 

 that the ratio t/X will remain constant when the strength of 

 the controlling field is varied, provided that I and N remain 

 constant. N, it is to be noticed, allows for the damping 

 caused by the viscosity of the air and the suspension, and by 

 the eddy-currents, and is therefore so far as the last cause is 

 concerned a function of M, the magnetic moment of the swing- 

 ing needle, and consequently will not remain constant if the 

 strength of the controlling field affects the strength of the 

 needle. We have then the following possible explanations of 

 the variation of the ratio : — 



1. I may not be constant. — This may occur through the 

 controlling magnet deflecting the swinging system 

 slightly from the vertical, and thus altering the axis 

 of rotation : this is more likely to occur when the field 

 is varied by moving the controlling magnet in 

 a horizontal plane than when it is varied by moving 

 the magnet up and down in a vertical plane passing 

 through the needle. 



it* 



