174 



appearance of solar spots was connected with a more copious eiTiis» 

 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 in- 

 vestigation of this kind, however, is not susceptible of any great de- 

 gree 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 greatest 

 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 the 4th of January, 1845. Mr. Alexander had 

 observed, a kw 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 teles- 

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

 the pile. The spot was very clearly defined, and might have. been 



