154 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



but between the wires themselves. It is evident, he states, 

 that, as every molecular disturbance produces an electric al- 

 teration, so, conversely, every electric current passing near 

 or through a substance produces a molecular change; a 

 change that is conspicuously shown by the phenomena of 

 electro -torsion, lately discovered by him. The molecular 

 changes referred to last as long as the current does ; thus a 

 rod of iron, when under the influence of an electric current, 

 emits a different sound, when struck, from that emitted by it 

 when the current ceases. The electric repulsion must, he 

 concludes, be due to a direction of structure different from 

 that which obtains when electric attraction is observed, and 

 he would propose to substitute this view for the theory of 

 Ampere, as ordinarily accepted. According to this new 

 theory, a magnet, like a spring, is not a source of power, but 

 only an arrangement for storing it up, the power being re- 

 tained by some internal disposition of its particles, acting 

 like a ratchet, and termed coercive power. According, also, 

 to this view, any method which produces the requisite direc- 

 tion of structure in a body will impart to it magnetic proper- 

 ties; thus a crystal of cyanite possesses the property, while 

 freely suspended, of pointing north and south by the direct- 

 ive influence of terrestrial magnetism ; and one of stanite 

 points east and west under the same conditions. 12 A y 1874, 

 IX., 434. 



NEW MAGNETIC CHART OF THE NORTHERN HEMISPHERE. 



To many of our readers the question will have often recur- 

 red as to what has been done with the great mass of obser- 

 vations bearing on terrestrial magnetism made in connection 

 with the Magnetic Survey which was so laboriously carried 

 on from 1840 to 1845. Few besides those acquainted with 

 the subject, however, are aware that for nearly forty years 

 Sir Edward Sabine has devoted himself (assisted, we must 

 not fail to say, by his wife) to the computations and investi- 

 gations needed in order to properly utilize the mass of ob- 

 servations accumulated during these five years. From time 

 to time, of late years, a contribution to terrestrial magnetism 

 has issued from his pen, and the last of these (No. 13) has 

 just been received in this country, bearing the title of "The 

 Magnetic Survey of the North Polar Regions of the Globe." 



