the Invention of the Telescope. 13 



gical fact, is everywhere else very particular in that respect. 

 It certainly is not, as Dr. Moll would have us believe, a 

 mere optician's report of the performance of his telescopes, 

 but is "the excellent evidence", by means of which the dis- 

 coveries of John and his father, "redounding so much to the 

 credit of themselves and their country ", were to be supported. 

 What is the meaning of that remarkable expression, "there 

 are no means of confirming his statement by other evidence"? 

 What was it that required adtlitional proof? As Dr. Moll 

 most truly observes, "Thousands, certainly hundreds, saw the 

 satellites in 1655; and why should not John, like other people?" 

 That which struck me as remarkable was not that John should 

 have seen them whenever he wrote, or was supposed to write, 

 that letter, but that in 1655 Borel should think worth while to 

 insert amongst his " excellent evidence " a declaration that he 

 had ; accompanying it with the cautious remark, that he had 

 no proof of it beyond John's own assertion. This observation 

 acquires additional force from the correction, for which I am 

 indebted to Dr. Moll, that John's whole letter is not given ; and 

 therefore it is to be presumed that Borel extracted from it only 

 that which he thought important. Surely the mere fact that 

 Jupiter's satellites were visible in his glasses did not merit that 

 distinction in 1655: if they were not, his trade would scarcely 

 have found him a livelihood. If he wanted to give a proof /ioxo 

 vmch his glasses were capable of showing, it would have been 

 more decisive of their excellence to declare whether or not he 

 had ever seen Saturn's satellite, then recently discovered by 

 Huyghens, of which discovery Borel gives an account in this 

 same book. Even in mentionmg the satellites, he would have 

 said simply, " 1 have seen Jupiter's satellites ", and would not 

 have given all the particulars of seeing sometimes four, some- 

 times two, or three, &c., unless he was speaking, or wished to 

 be understood as speaking, of something of which he had never 

 before heard. Mr. Dollond or Mr. Tully (if I may be allowed 

 to borrow Dr. Moll's own illustration), should they "be asked 

 at the present day for an account of their best glasses, would 

 scarcely think of stating that there is something like a ring 

 round Saturn ; and that, so far as they can judge, it appears 

 to revolve about the planet: nor, if they should communicate 

 such information to Dr. Moll, would it occur to him to quote 

 it as "excellent evidence" of the discoveries of these gentle- 

 men. It was not more to the purpose in 1655 to print John's 

 remark, that, so far as he tould tell, there were four satellites 

 which appeared to circulate round Jupiter; since the fact that 

 they did so had been indisputal)ly established more than forty 

 years, dieir periods had been calculated, and their iiilure ap- 

 pearances predicted ; — unless indeed there was a concealed in- 

 tention ofsiiggcsling the idea at some future period, that John 



