Scientific Lectures. 173 



seems to depend upon the condition of the sun's surface. We owe 

 this astonishing discovery to the labors of three men. First, Coun 

 selor Schwabe, of Dessau, Germany, began, in 1820, daily observations 

 on the number, size, and position of the spots which are nearly 

 always visible on the solar disc. With an admirable perseverance, 

 worthy of his nation, he has kept these up for forty-six years. This 

 long siege at last made the sun reveal the order of his changing 

 appearance, and in 1850, Schwabe announced that the amount of 

 spotted surface, which yearly appeared on the sun, followed a regular 

 law, going through a cycle in about ten years. Thus, in 1860 the 

 number of spots visible was remarkable ; then in 1865 very few were 

 to be seen ; after this they became more and more frequent, until 

 1870 they again appeared in profusion. About the same time that 

 Schwabe gave this discovery to the world, Professor Lament, oi 

 Munich, announced that the daily range of the needle's vibration 

 went through a similar cycle. Yery soon afterwards Gen. Sabine, of 

 England, discovered independently the same fact, which he deduced from 

 magnetic observations made at places so far removed from each other 

 as Toronto in Canada, and Hobarton in Yan Dieman's Land, and was 

 thus led to refer the cycle to some cause exterior to the earth, and 

 then pointed out the coincidence of the ten year solar spot 

 cycle, and that of the maget's daily range of deflection ; which latter 

 at Gottingen, for example, is 4' more during the year of the greatest 

 number of spots than during the year of the least. 



But we have said that the needle is subject to unruly vibrations, 

 coming at unexpected times, and affecting, simultaneously, magnets 

 suspended at great distances from each other. These disturbances are 

 often, though not always, accompanied by outbursts of the aurora 

 borealis, and it has been observed that the regular flashes and lateral 

 movements of the auroral columns are always accompanied by simul- 

 taneous deflections of the suspended magnet. 



The direction of present research in these interesting problems is 

 to find a relation of concurrence between the sudden changes on the 

 sun, now visible by the aid of the spectroscope, and sudden deflections 

 of magnets suspended at many points on the earth's surface. This 

 problem, however, is yet far from solved, and I will therefore merely 

 make this hint as to its attractiveness and its importance.* 



Again let us return to the contemplation of our magnetic curves, 

 whose paths have already conducted us to some very important truths. 



♦Explosion on the Sun, C. A. Young, Ph. D. ; Amer. Jourl. Sci., Dec, 1871, 3d series, vol. ii, p. 

 4C8. Compare this with Magnetometer Indications on September 7th, by C. A. Young, Ph. D. ; 

 Amer. Jourl. Sci., 3d series, vol. iii, p. 69. 



