[ 230 ] 

 XLIV. Intelligence and Miscellaneous Articles. 



EXPERIMENTS ON THE SPOTS ON THE SUN. 



AT the meeting of the American Philosophical Society, June 20, 

 1845, Prof. Henry of Princeton, U.S., made the following 

 communication of a series of experiments made by himself and Prof. 

 Alexander relative to the spots on the sun. 



His attention was directed to this subject, by an article in the Sep- 

 tember number of the Annates de Chimie, by M. Gautier, upon the 

 influence of the spots on the sun on terrestrial temperature. It is 

 well known that Sir William Herschel entertained the idea, that the 

 appearance of solar spots was connected with a more copious emis- 

 sion of heat, and that the seasons during which they were most abun- 

 dant were most fruitful in vegetable productions ; and pursuing this 

 idea, he was led to trace an analogy between the price of corn and 

 the number of solar spots during several successive periods. The 

 result of this investigation, so far as it was extended, seemed to fa- 

 vour the views of this distinguished philosopher. A mode of inves- 

 tigation of this kind, however, is not susceptible of any great degree 

 of accuracy ; the price of corn is subject to so many other causes of 

 variation besides that of solar temperature, that little reliance can be 

 placed on it. 



M. Gautier has attempted to investigate the influence of the solar 

 spots on terrestrial temperature, by comparing the temperature of 

 several places on the earth's surface, during the years in which the 

 spots were most abundant, with those in which the smallest number 

 were perceptible. From all the observations collected, it seems to 

 be indicated, that during the years in which the spots were the great- 

 est in number, the heat has been a trifle less ; but the results are far 

 from being sufficiently definite to settle the question : and M. Gautier 

 remarks, that a greater number of years of observation at a greater 

 number of stations, will be necessary to establish a permanent con- 

 nexion between these phenomena. 



The idea occurred to Prof. Henry, that much interesting informa- 

 tion relative to the sun might be derived from the application of a 

 thermo-electric apparatus to a picture of the solar disc, produced by 

 a telescope, on a screen, in a dark room. This idea was communi- 

 cated to Prof. Alexander, who readily joined in the plan for reducing 

 it to practice. It was agreed that they should first attempt to settle 

 the question of the relative heat of the spots as compared with the 

 surrounding luminous portions of the sun's disc. The first experi- 

 ments were made on trie 4th of January 1845. Mr. Alexander had 

 observed, a few days previous, a very large spot, more than 10,000 

 miles in diameter, near the middle of the disc. To produce the image 

 of this spot, a telescope of four inches aperture, and four and a half 

 feet focus, was placed in the window of a dark room, with a screen 

 behind it, on which the image of the spot was received. The instru- 

 ment was placed behind the screen, with the end slightly projecting 

 through a hole made for the purpose, and a small motion of the te- 

 lescope was sufficient to throw the image of the spot off or on the end 



