14S ON THI TELESCOPE, 



Obfervations He was looking at the liars with a friend on the bridge art 

 'mSoJ°ot hE th c Pra § ue ' and they obferved one in particular. « Vidi" * he 

 ttlefcope. ^ys, " ftellam fub urfa, majorem cseteris per perfpicilla intu- 



itus, quae aequale caeleris fixis lumen mihi fine perfpicillis 

 diffundere videbatur." It is not likely that the perfon, who 

 mentioned the flrft ufe of fuch an inftrumenl as a telefeope, 

 would confine himfelf to lb dry an account of the effefts pro- 

 duced by it. But there is another argument, which may be 

 drawn from the book itfelf, and that is, when Kepler is giving 

 an account f of his obferving a comet in the year 1618, he 

 ufes the word telefcopium and not perlpicillum. " 6 Sept. 

 jam nulla amplius cunda vilu nudo potuit obfervari et telefco- 

 pio infpe&us fatis magnus apparuit." " Sept. 23. Planitudo 

 major tine telefcopio, quam per illud."X 



But what puts it beyond doubt that Kepler was not in pof- 

 fetlion of a telefeope fo early as the year 1607, is that we hear 

 of no great difcoveries which he made about that time by ob- 

 ferving the heavens. Montieur de Moutucla, indeed, fays § 

 that " Uniquement applique a determiner avec precifion les 

 mouvemens celeftes, cet hommecelebre faiioit peu d'ufagedu 

 telefeope." He probably thought himfelf juftified in this, 

 when others were employed in the more mechanical labour of 

 obfervation. When he had no fuch fellow-labourers, it is im- 

 poilible that a man like Kepler could have neglected an oppor- 

 tunity of obferving, or have concealed the means of doing fo; 

 and if he had not done both, we mud have had fome notices 

 remaining either in his own writings or thofe of others.. 

 We muft recol!e£t likewife, that he was the firft who under- 

 ftood the theory of telefcopes and the combination of lenfes, 

 and we muft not forget, that thefe difcoveries being once made, 

 the greatefi difficulty was overcome ; it was only neceflary to 

 ufe the telefeope and mark the objects which it prefented to 

 the fight. 



From what I have dated there feems to be confiderable dif- 

 ficulties attending either of the ways, which have been pro- 

 pofed for interpreting the word perfpicilla. But there are 

 fome pafiages in the Sidereus Nuntius, which feem to aflift us 

 in affixing a meaning to the word, lefs exceptionable than the 

 one hazarded by Aletes. 



» — Sept. 1607. + P. 48. J P. 52. 



§ Hiftoric des Mathematiques, vol. XI. p. 234. 



In 



