60 The Magnetism of Basalt. 
The next table gives the initial, maximum, minimum, 
and final values of the susceptibility for each heating, along 
with the temperatures of the maxima and minima. The 
last column gives the percentage increase in susceptibility 
between the temperature of the air and the temperature of 
maximum susceptibility during heating. 



















| ob | 
| 4 : aa : yhoo fea 
Cr a: | MM | Bi | 
OS Be Np de afi) 2a 
Bar. Se | ge | — | £ | $40 ee 
| Te ce mS < a | eS 
Rowley Blue. | | | ) 
NOMI Cra. 0053 | 0056 = 0005 |-0057 | 185 | 550 | 6 
(10th heating) | | 
INOmo. Wueee "0064 | 0087 | :0009 | 0009 , 340 | 500 36 
(Ist heating) | : | 
INO ee | 0017 | -003 ‘0008 | 0022 | 480 | 540 82 | 
(6th heating) | | | | | | 
Rowley Dolerite. | | | | | 
NORM Ae 0058 | 0087  -0004 |-0013 | 260 | 597 50 
INON2isceeee | 0059 | ‘0089 = 0009 | 0009-360) | 619 | 51 
Dattenberg. | | | | | 
Nowe ie Sa. 0056 | 0059 = 0011 | 0056 | 932 500 | 5 
(2nd heating) | | | 
Norte 0058 | ‘0060 | 0010 | 0089 45.0} ll 3 
(5rd heating) | | | 
NOs 2 aes. ‘0013 | 0042 0010 |-0031 | 140 | 260 | 228 
NOMS Asc 100255) :0030;— | 0002 |) 22 9) 668-7 aan 20 
iodo 4t 0048 ; 0050 |-0002) ... | 48 | 250 4 
INGiDe oa | C083 | 00427 3/0004 | 2. 4 Wor see ey | 
Magnetite...... 0166 | 0214) | -0003 | -0126 | 280) | 552 | 29 
| 0206 f | | Pet iOeM 




The values found for the susceptibility of Rowley basalt 
are much greater than those given by Prof. Riicker in the 
paper mentioned at the beginning ; but differences quite as 
great present themselves in the values found for the five 
Dattenberg bars. 
In the same paper Prof. Riicker gives a theory of regional 
magnetic disturbances, the latter being explained by the 
magnetism of the rocks. By assuming that the tempe- 
rature increases 1° for every 90 feet, a depth of 12 miles is 
found, below which magnetic matter ceases to exist. Now 
A. Harker has objected*, on geological grounds, to the as- 
sumption of a thickness of 12 miles, and puts the depth at 
5 of this amount. Prof. Riicker shows, however, that the 
* A. Harker, Proc. Camb. Phil. Soe. vol. x. pt. 5 (1900). 
siiin mati macegniadll 
