2 PHILOSOPHICAL TRANSACTIONS. [aNNO 1665. 



A71 Account of Camp AN fs Improvement of Optic Glasses ^ 



N' 1, p. 2. 



The improvement of optic glasses, not long since attempted at Rome by 

 Signer Giuseppe Campani,* is described in a book, entitled, Ragguaglio di 

 nuove Osservationi, lately printed in the said city, in which the following 

 particulars are contained: — 



The first regards the excellence of the long telescopes, made by the said 

 Campani, who pretends to have found a way to work great optic glasses with a 

 turn-tool, without any mould. And it having hitherto been found by ex- 

 perience, that small glasses are in proportion better to see with, on the earth, 

 than large ones; that author affirms, that his are equally good for the earth, 

 and for making observations in the heavens. Besides, he uses three eye- 

 glasses for his great telescopes, without finding any Iris, or such rain-bow 

 colours, as usually appear in ordinary glasses, and prove an impediment to 

 observations. 



The second concerns the circle of Saturn, in which he has observed nothing, 

 but what confirms M. Huygens's Zulichem system of that planet, published by 

 that worthy gentleman in the year 1659. 



The third respects Jupiter, in which Campani affirms he hath observed, by the 

 goodness of his glasses, certain protuberances and inequalities, much greater 

 than those that have been seen there hitherto. He adds, that he is now 

 observing, whether those sallies in the said planet do not change their situation ; 

 which if they should be found to do, he judges that Jupiter might then be said 

 to turn upon his axis; which, in his opinion, would serve much to confirm the 

 opinion of Copernicus. Besides this, he affirms, he has remarked in the belts 

 of Jupiter, the shadows of his satellites, and followed them, and at length seen 

 them emerge out of his disk. 



* There were two brothers (Matthew and Joseph) of this name, Campani, residing in Rome in 

 those times, botli very eminent for their mechanical contrivances of optical and philosophical in- 

 struments, and for several treatises on such subjects ; particularly relating to pendulums, or time 

 pieces, for the longitude ; also to spectacles, and to telescopes, of which it is said they made the very 

 best and largest in their time ; being then as famous for their refracting telescopes, as Herschel is 

 now for his large reflectors. It is said it was by their telescopes that the first Cassini made his best 

 observations and chief discoveries in tlie heavens ; and they still show at Paris, among the astrono- 

 mical antiquities, several of Campani' s object glasses, of eight, ten, and twelve inches diameter. — 

 Other circumstances relating to their telescopes maybe seen in several parts of these Transactions) as 

 inN°'4, 8, 12, &c. 



