NATURAL PHILOSOPHY. 95 



the sun, inasmuch as they obey a daily law, and are moreover 

 independent of the light of the sun. They have a yet still more 

 mysterious relation with our luminary. Schwabe, of Dessau, having 

 for nearly forty years watched and recorded the spots on its disc, saw 

 that these spots exhibit a maximum and minimum nearly every ten 

 years ; and General Sabine having discovered that magnetic disturb- 

 ances have also a ten years' period, fortunately thought of comparing 

 the two periods, and found that they were precisely the same, having 

 the same years of maximum and minimum. This brought us into the 

 presence of some great cosmical bond, other than gravitation. On one 

 occasion the sun was believed to be caught in the very act of causing a 

 magnetic disturbance. On Sept. 1st, 1859, Messrs. Carrington and 

 Hodgson, independently, observed a bright sun spot, and at the very 

 same moment the magnets at Kew were found to be suddenly disturbed. 

 It has also been proved that these disturbances are accompanied by 

 auroras and also by electric earth-currents, in some cases interfering 

 with the telegraph wires, both having a ten-yearly period. The na- 

 ture of the bond by which these phenomena are allied is still a pro- 

 found mystery. Mr. Stewart, however, with diagrams and models, 

 endeavored to elucidate it by the application of the laws of induced 

 primary and secondary electric currents, demonstrated by Faraday. 

 The earth, being considered as the iron core of an electro-magnet, is no 

 doubt excited by some primary current (probably in the sun), and, 

 having a conductor in the upper and rarer strata of the atmosphere, and 

 another conductor round it in the upper and moist crust of the earth, 

 has also an insulator in the lower and denser strata of the atmosphere. 

 Mr. Stewart considers that every time a small but rapid change takes 

 place in" the magnetism of the earth, it gives rise to a secondary or in- 

 duced current in the two conductors ; and this occasions the electric 

 earth-currents and auroras, probably due to the inequality of the 

 earth's surface. With regard to the spots on the sun's disc, Mr. Stew- 

 art suggests that, if that luminary, by causing magnetic disturbances, 

 is capable of producing auroras in the earth's atmosphere, it is surely 

 capable of producing similar phenomena in its own. 



CAUSES OF FAILURE IN SUBMARINE TELEGRAPH CABLES. 



A recent article in the London Times states several important facts 

 in -reference to the causes of failure in various submarine telegraph ca- 

 bles, and in respect also to the precautions now taken to prevent future 

 similar disasters. 



" Every operation in submarine telegraphy even the great Atlan- 

 tic line has contributed its quota of valuable experience ; for, though 

 snccessfully laid by Sir Charles Bright and his assistant engineers, in 

 spite of its imperfect construction, it was destroyed % the injudicious 

 electrical treatment it received after submersion. This fact is now so 

 well established that the cause of the failure of the Atlantic cable may 

 be considered as set at rest forever. The insulation of that line was 

 not very perfect, as may be imagined from the infancy of the science 

 at that time, but yet the electrical power used was such as would in- 

 fallibly break down even the most perfect cables manufactured at the 

 present day. Of this our readers may judge when it is stated that the 

 large induction coils first used in signalling between England and 



