146 HERSCHEL AND HIS WORK 



hemisphere will remain unexplored as will take up 

 213 years more to examine." In these numbers il<r- 

 schel was perhaps mistaken. Struve at Pulkowa found 

 80 nights suitable out of 120 clear nights; but Sir 

 John Herschel'R experience at the Cape of Good Hope 

 gave him the whole or parts of 131 nights in 1836, 

 and at least 100 in the following year. The estimate 

 of 598 years, or rather 811, by Sir William Herschel 

 may be set down as excess! \ 



Herschel does not appear to have been altogether 

 satisfied with the position he had taken up. It 

 was not warranted by pure and inductive science. 

 The foundation on which alone he could build with 

 confidence had not been laid, the distance of fixed stars 

 and nebulae. "To these arguments," he says, "which 

 rest on the firm basis of a series of observation, we may 

 add the following considerations drawn from analogy." 

 Science demands something more trustworthy than 

 arguments and analogy. Mathematical science is not 

 content with probability : it demands demonstration, and 

 this he could not give. He had a distinct idea of an 

 ocean, we shall say, of ether, transmitting light. In that 

 ocean are thousands of floating islands, each composed 

 of myriads or millions of shining worlds, all communi- 

 cating with each other by far-piercing sunbeams. 

 What the telegraphic messages thus sent from sun to 

 sun, from island to island, may be, Herschel had no 

 means at first of knowing. He came to understand 

 and even read some of these messages in later years. 

 We are able to read more of them now, for they tell 

 the sizes of suns, their rates of motion, their dii - 

 of motion, and other pieces of star history incredibly 

 interesting to curious man. Herschel did not imagine 



