C. GENERAL PHYSICS. 171 



extraordinary event, but not unprecedented. In all such in- 

 stances the fracture seems to follow a plane passing through 

 a comparatively sharp angle at the side of a collar, or at the 

 end of a journal. 



ATOMIC HEAT. 



Professor F. W. Clark, the author of the table of phys- 

 ical constants recently published by the Smithsonian Insti- 

 tution, states that he is now compiling a table of the atomic 

 heats, so called, and that, in the course of a comparison of 

 over four hundred values, he has found that while, on the 

 one hand, the laws of Dulong and Petit are approximately 

 verified (namely, that the atomic heats of atoms are con- 

 stant), yet, on the other hand, the deviations from this law 

 are also worthy of notice; inasmuch as if we arrange any 

 group of allied substances in the order of their molecular 

 weights, we at once find the deviations from the approxi- 

 mate law to be themselves governed by the simple rule that 

 they are greater in proportion to the increase in the atomic 

 weights. It follows, therefore, that if the bodies in question 

 could have their specific heats determined under similar cir- 

 cumstances, i. e., at corresponding temperatures above their 

 own individual boiling-points, we should derive numbers 

 much more nearly constant than those now accepted. Bul- 

 letin of the Phil. Soc. of Washington. 



THE EFFECT OF GALVANISM OX A MAGNETIZED WIRE. 



As the result of some preliminary experiments on a mag- 

 netized copper wire, Professor Balfour Stewart states that 

 when a galvanic current passes through a magnetized wire 

 there is a first effect in the direction of increased resistance, 

 which appears to have reference to three things, namely, the 

 previous state of the wire, the solidity of the circuit, and its 

 magnetization. In the second place, we have an average ef- 

 fect, apparently exhibited in a decreased resistance, while the 

 magnetism is on, without reference to the direction of the 

 magnetism. In the third place, when in a solid circuit the 

 direction of the magnetism has been recently changed, there 

 appears to be a temporary reversal of the average effect, 

 which appears at first as an increase of resistance. Fourth, 

 we have also some evidence that a copper wire, one end of 



