54 Dr. G. E. Allan on 
Current. in 
ice agent SS a 
amp. mm. ohms. mm. 
h m 30 cells. 
OATES 2. Ae ee 1-160 fel | 19-0 16-7 
cere Sey ees 1:160 ke | 187 D3 
25 cells 
pal oe haere 1160 ae : 18-0 13:0 
2 rg eae 1-160 a t 17-4 13:0 
31 as 5S aes 1-160 ee \ 17-0 1255 
Furnace current off. 
Ss ian, SO 1-160 oes \ 160 128 
DO ae eee tee 1-160 se \ 140 12:5 
213 ae eae ents ae 1162 ae i 12-0 12-5 
Men Oem a ae 1-163 Bee \ 10-0 | 11-9 
5 ANNs eee Uoeee 1163 7 3 8-5 IL-7 
i) Rae One aie os mets rei iis 
Thermometer and basalt removed from furnace. 
| ae sera aoe +1:168 ira Coil effec) aes 
From the above figures, which are those for the sixth 
heating of Rowley Blue No. 2, it may be seen that whilst 
the temperature was made to vary rapidly at the beginning 
and at the end of the experiment, previous work haying 
shown that there was very little change in the susceptibility 
of the bar under test up to about 300° C., the rate of heating 
or cooling was slowed down as the temperature of maximum 
or minimum susceptibility was approached, the temperature 
change in the furnace being reduced to 2° or less per minute. 
The effect due to the coils alone having been almost constant 
throughout the experiment, 1:‘7 mm. were added to each 
deflexion. The deflexions were then calculated for a current 
of 1:15 amperes in the magnetizing coil, and these plotted 
with the temperatures. 
The experiments on Rowley blue basalt No. 2 show that 
during the first heating the susceptibility increases to a 
maximum at about 340° C., and then diminishes, at first 
slowly, then rapidly, until a minimum is reached at about 
500° C. As the bar cools it does not regain its magnetic 
qualities, but, after passing through a maximum point at 


