C. EF. Dutton— Hawaiian Volcanoes. 219 
The two readings differed by several centimeters on the galva- 
nometer scale. The experiment was repeated and always with 
a like result. 
There was no room for doubt that the direction of the equi- 
potential lines in the steel was permanently changed by the 
action of the magnet. This change was in the same direction 
however, as indicating that the rotational effect is not due to 
the mere mechanical stress to which the metal is subjected in 
the magnetic field, for though no one has ever pointed out how 
any such stress could produce the effect observed, many have 
no doubt questioned whether it might not after all be due in 
some obscure way to such stress. 
t may be stated incidentally that the transverse effect 
appears to be much greater in steel of blue temper than in soft 
iron, and again much greater in steel of very hard temper than 
in steel of blue temper. If we call the effect in soft iron 1, the 
effect in blue steel is perhaps 2, and that in very hard steel 4. 
Art. XX VI.—Recent Exploration of the voleanie Phenomena of 
the Hawaiian Islands ; by Captain C. E. Durron. (From a 
letter to J. D. Dana, dated Washington, D.C., Feb. 8, 18883. 
hates it. The soutbern district of the island, Kau, is almost 
