352 A Short History of Astronomy [CH. xn. 



variation in the number of spots and possibly of other 

 markings on the sun suggesting to him the probability 

 of a certain variability in the total amount of solar light 

 and heat emitted. The terrestrial influence of this he 

 tried to measure in the absence of precise meteoro- 

 logical data with characteristic ingenuity by the price of. 

 wheat, and some evidence was adduced to shew that at 

 times when sun-spots had been noted to be scarce 

 corresponding according to Herschel's view to periods 

 of diminished solar activity wheat had been dear and 

 the weather presumably colder. In reality, however, 

 the data were insufficient to establish any definite con- 

 clusions. 



270. In addition to carrying out the astronomical re- 

 searches already sketched, and a few others of less import- 

 ance, Herschel spent some time, chiefly towards the end of 

 his life, in working at light and heat ; but the results obtained, 

 though of considerable value, belong rather to physics than 

 to astronomy, and need not be dealt with here. 



271. It is natural to associate Herschel's wonderful series 

 of discoveries with his possession of telescopes of unusual 

 power and with his formulation of a new programme of 

 astronomical inquiry ; and these were certainly essential 

 elements. It is, however, significant, as shewing how im- 

 portant other considerations were, that though a great 

 number of his telescopes were supplied to other astro- 

 nomers, and though his astronomical programme when 

 once suggested was open to all the world to adopt, hardly 

 any of his contemporaries executed any considerable 

 amount of work comparable in scope to his own. 



Almost the only astronomer of the period whose work 

 deserves mention beside Herschel's, though very inferior to 

 it both in extent and in originality, wzsjohann Hieronymus 

 Schroetcr (1745-^16). 



Holding an official position at Lilienthal, near Bremen, 

 he devoted his leisure during some thirty years to a scrutiny 

 of the planets and of the moon, and to a lesser extent of 

 other bodies. 



As has been seen in the case of Venus ( 267), his results 

 were not always reliable, but notwithstanding some errors 

 he added considerably to our knowledge of the appearances 



