
WIM Ml Ny a 
46 Dr. G. E. Allan on 
of magnetite. But this, although in a certain measure true, 
is not always the case. 
Messrs. Barton and Williams found in 1892 that magnetite 
has a maximum susceptibility at 825° C.* and a minimum at 
557° +, whilst P. Curie {, in 1895, using a rougher method, 
found its temperature of magnetic transformation to lie in 
the neighbourhood of 535° C. 
The basalt specimens were obtained from two localities, 
Rowley Regis near Birmingham, and Linz on the Rhine. 
‘Two kinds were obtained at Rowley, being known locally as 
the blue and grisly grey. The former variety resembles the 
ordinary basalt, whilst the latter is formed of much larger 
crystals and is a dolerite. The German basalt, which I was 
enabled to obtain through the instrumentality cf the late 
Herr Boden of Rotterdam, and which the Basalt Company 
of Linz gave me every facility to choose, was also a finely 
crystalline dark blue variety (being, indeed, similar in cut- 
ward appearance to the Rowley blue basalt) and was obtained 
from the above Company’s quarry on the Dattenberg. 
The magnetic tests were made on bars cut from ‘pieces of 
the above-named rocks to a pattern 10°5 cms. long by 1°5 em. 
square, the expense of the cutting being defr ayed by a grant 
made by the Birmingham Philosophical Society. 
Method and Apparatus. 
The magnetometric method was chosen as being probably 
the most convenient for testing different rock specimens 
Fig. 1.-—Combined magnetizing-coil M M and electric furnace Pe 
with water-jacket AB. 


under similar temperature conditions from time to time, and 
the temperatures were measured by means of a platinum 
thermometer. Accordingly a combined magnetizing solenoid 
* I. H. Barton & W. Williams , Electrician, vol. xxix. p. 432 (1892). 
+ E. H. Barton & W. Williams, Biayks Report, Edinburgh, 1892. 
t P. Curie, Ann. de Chim. et de ’Phys. vol. v. ser. 7,-p..289 (1898). 
