446 
DR. J. HOPKINSON OR MAGNETIC AND OTHER PHYSICAL 
Mather and Platt. I have no analysis of its composition. I asked for the softest 
iron they could supply. 
The dimensions of the ring were as shown in tlie accompanying sketch 
The area of section is Pl)05 sq. cm. The area of the middle line of the secondary 
coil is estimated to he 2‘58 sq. cms. This estimate is, of course, less accurate than 
the area of section of the ring itself. 
The secondary coil had 48 convolutions, the primary 100 convolutions. 
At the beginning of the experiments the insulation resistance of the secondary 
from the ]3rimary was in excess of 1 megohm; the resistance of the secondary and 
the leads was 0’692, the temperature being 8°’3 C. 
The resistance of the leads to the secondary and of the part of the secondary 
external to the furnace was estimated to be 0'04. 
A curve of magnetisation was determined at the ordinary temperature on the 
virgin sample with the following results, shown graphically in Curve I. ; in each case 
the observation was repeated twice with reversed direction of magnetising currents, 
and the kicks in the galvanometer were found to agree very closely together :— 
Magnetising force . 0‘15 0‘3 0'6 I'2 2’2 4'4 8'2 I4’7 24'7 37'2^ 69‘2 
Induction per sq. cm. 39'5 116 329 1,660 6,041 10,144 12,633 14,059 14,702 15,149 15,959 
The ring was next heated and observations were made with a magnetising force of 
8‘0 to ascertain roughly the point at which the magnetism disappeared. After the 
magnetism had practically disappeared and the temperature was roughly constant, as 
indicated by the resistance, being 2‘92 before the experiment and 2'85 after the 
experiment, corresponding with temperatures of 838° C. and 812° C., the induction 
was determined for varying magnetising forces. 
Magnetising force . . . 2'4 4'2 8'0 21'0 49‘8 
Total induction .... small 12’3 22'7 58'2 143 
This shows that the induction is, so far as the experiment goes, proportional to the 
inducing force. 
Taking the total induction as 143, corresponding to a force of 49'8, have 
* [Added July 2, 1889.—Sir Joseph Whitworth and Co. have since kindly analysed this samjile for me 
'with tLe following result:— 
C Mn S Si P Slagt 
Percent. . , . ‘OlO -143 '012 Nil '271 ‘436 - 
. t Containing 74 per cent. SiOo (Silica).] 
