ON THE TELESCOPE. 147 



obfervationum Tychonicarum errores ex nudorum Dioptrorum Observations 

 ufu necedarie confequuntur." Now it is only neceflary to ex- relatin S t0 the , 



., . .. • T n **•!• i „ , lf invention ef the, 



amine the Attronomiae Initauratce lYLechanica, and we (hall leetdefcope. 

 that almoft all the inflruments, which Tycho Brahe ufed, are 

 fitted with fights, which were fome perforated with fmall 

 holes, and fome divided by narrow flits: this part of the in- 

 ftrument he called dioptra, the perforations he cal led foramina, 

 and the flits rimulce. 



I could quote further proof that thefe words were commonly 

 ufed in the fenfes which I have affixed to them, but it would 

 be not only unneceflary but tedious. It mult, therefore, re- 

 main with Aletes to produce as good authorities for the al- 

 ledged difference between perf pic ilium and ptrfpicillum vitreum. 

 I cannot help thinking, however, that the very title-page of 

 Kepler's Dioptrice will be fatal to his explanation; for there 

 we find that mention is made of the difcoveries of Galileo, 

 made " ope perjpicilli" after the publication of the Siderius 

 Nuntius. Here the word perfpicillum is undoubtedly ufed for 

 the telefcope itfelf, and before I conclude what I have to fay, 

 I fhall quote a paflage from Galilceo, which is flill more con- 

 tradictory to the ideas of Aletes. 



Although I differ from your correfpondent with refpeel: to 

 the arguments, which he has ftated to you, flill I agree with 

 him in his general conclufion, that Kepler did not mean a te- 

 lefcope by the word perfpicilla. We learn, indeed, from 

 Borelli's book de vero inventore telefcopii, that * one account 

 makes the invention as early as the year 1590; but when we 

 compare this with the depofition of Sara Gaedardat and what 

 is. ftated by Galileo in (p. 10 of) his Sidereus Nuntius, it feems 

 moll probable that telefcopes were not known before the year 

 1609. If Zachary Jaufens was acquainted with them before 

 that period, he feems not to have publifhed his difcovery to 

 the world. Now Kepler, in the place above quoted from the 

 dedication of his Dioptrice, takes an opportunity of praiflng 

 the invention in the higheft terms, and as he did this, when it 

 was public, it is probable that he would have done fo flill 

 more warmly, if he had been the fir ft who publifhed an ac- 

 count of obfervations made with them ; but there is nothing 

 of this kind in the paflage alluded to in his book de cometis. 



* P. 25. f p. 31. This makes the invention about 1611 or 

 1613, but " de certo prsefixo tempore nonpotuit dicere." 



L2 He 



