Dr. Moll on the Invention of Telescopes. 493 



never read Borel's book with sufficient attention, and, as the 

 book is scarce, he knows it perhaps only from quotations. 

 There is no letter inserted in it from John, the son of Zacha- 

 rias ; but in answer to some queries either from Boreel or 

 from Borel, he gives two memorials or notes of what a tele- 

 scope of his making could show. In the first place, he men- 

 tions the appearances and dark places in the moon ; and it is 

 to be observed, that what he says of the appearance of the 

 moon seen through his telescope, answers exactly to what one 

 would expect of a good instrument. It plainly shows, says 

 John, the moon to be a sphere, with distinct edges, and not a 

 plane. The following is his statement of Jupiter's satellites : 

 he often observed the planet which shows itself round, well 

 defined, and spheric ; near it he often saw two highly situated 

 small stars, sometimes he saw three, and generally four of 

 these small stars. As far as he could observe, they go perpe- 

 tually in circles round Jupiter ; but he adds, this I leave to 

 astronomers to determine, for it is not, says he, my business to 

 make astronomical observations, but to furnish astronomers 

 with telescopes as good as I am able to make. 



I challenge the author of the life of Galileo to point out the 

 passage in Borel's book in which either Boreel, or John, the 

 optician, exhibit the least intention of throwing Galileo's disco- 

 veries in the shade. But it may be permitted, I should think, to 

 an optician, when asked by an ambassador at a foreign court, to 

 state what the performance of his instruments is ; and I believe 

 that neither Mr. Dollond nor Mr.Tully could be justly accused 

 of disparaging Sir William Herschel's merit, if they were to 

 state that the Georgium Sidus is visible in their telescopes. 

 John certainly says, in 1655, when he was fifty-two years of 

 age, that he often saw four satellites with a telecope of his own 

 making ; but he never says that he saw the satellites before 

 January 1610, the epoch of Galileo's discovery, nor does he 

 even mention when he first saw them. He is, says he, no 

 astronomer, but an optician ; and when this optician states, in 

 1655, that he makes telescopes with which the satellites can be 

 seen, it is difficult to understand how it can be inferred that he 

 made this statement in order to deprive Galileo of the honour 



