240 TKANSACTIOXS OF THE ^MAY 17, 



for several years. The relation between tliis periodicity and ter- 

 restrial conditions has been assiduously examined, but on the 

 whole the outcome seems to me to leave this connection as 

 doubtful as it ever was, in most cases at least. While in some 

 parts of the earth it looks as if there were a slight but marked 

 increase of storm and rainfall at the time of sun-spot maximum, 

 the reverse seems to be true in other countries. In South Amer- 

 ica, Dr. Gould thinks that he has demonstrated a very })ercei)ti- 

 ble effect of tiie condition of the sun's surface in modifying the 

 strength and direction of the winds ; but thus far similar inves- 

 tigations elsewhere show no such result. It will evidently be 

 necessary to wait for a longer and more widely extended collec- 

 tion of statistics to settle the question. We do not even know 

 as yet whether we get more or less than the average heat from 

 the sun during the sun-spot maximum. 



But I tliink it may be set down as certain that the condition 

 of the sun's suj-face exerts, if perhaps a real, yet only a very slight 

 effect upon our earthly meteorology. With terrestrial magnet- 

 ism the case is markedly and singularly different, and one of the 

 most interesting problems now pressing for solution is the nature 

 of the connection between sohir disturbances and magnetic 

 storms. 



Solar Heat. 



A great deal of labor has been expended upon the study of the 

 sun^s heat during the last decade. The investigations that 

 strike me on the whole as most worthy of mention are those of 

 our own Langley and of the Italian Rosetti, whose early death a 

 few months ago is a great loss to science. Secchi and Ericsson, 

 on the one side, had contended for a solar temperature of some 

 millions of degrees, basing their results on Newton's law of cool- 

 ing; while on the other, Ci'ova and Violle, from their measures of 

 the solar radiation, reduced according to the so-called law of 

 Dulong and Petit, maintained that tiie temperature does not 

 much exceed that of many terrestrial furnaces, somewhere from 

 1,500° to 2,500° C. Rosetti's experiments upon the radiation of 

 the electric arc and other sources of intense iieat, showed pretty 

 clearly the inapplicability of Dulong and Petit's law to high 

 temperatures, and indicate a solar temperature not far from 

 10,000° C, or 18,000° F. But they also make it clear that the 

 limits of uncertainty are still very great. 



Professor Langley, by his invention of the bolometer, has been 

 able to investigate separately the amount of energy transmitted 

 to the earth in tiie solar rays of every possible wave-length, and 

 to determine the effect of our atmosphere in absorbing each kind 

 of ray. He has shown that the older method of investigating 



