490 Dr. Moll on the Invention of Telescopes. 



more than three times the salary, which it was the custom to 

 give to a lecturer of mathematics. 



Thus we perceive the Venetian Senators doing in August, 

 1609, the same thing which the members of the slates-general 

 had done in October, 1608, about ten months sooner. They 

 ascended to high places for the purpose of gazing at distant 

 objects. Both the Dutch and the Venetian magistrates nobly 

 rewarded the invention, which was tendered to them. The 

 Venetians rewarded Galileo as a philosopher should be re- 

 warded, by an honourable station and independence. The 

 Dutch treated Lippershey in the best way an artist can be 

 treated ; they gave a high price for his article, and made large 

 orders for it. The date assigned by Viviani to these trans- 

 actions, the 25th of August, 1609, agrees completely with 

 what Lorenzo Pignoria wrote the 31st of August to Paolo 

 Gualdo, and which letter was mentioned above. 



It is exceedingly gratifying to observe, that Galileo almost 

 immediately brought the telescope with a convex object-glass 

 and a concave eye-glass, to all the perfection of which it is sus- 

 ceptible, without being achromatic. He observed with it all 

 that could be seen by its means ; he ascertained the power of 

 his glasses with great ingenuity, and he indicates the difference 

 between linear and superficial amplification with perfect ac- 

 curacy. His German biographer, Tagemann, does not seem 

 to have clearly understood this difference, for he appears to 

 imagine that Galileo's telescope really had a power of a 

 1000 times, whereas it was only of about 32. 



In a Galilean telescope the focal length of the object-glass 

 cannot go beyond a certain extent, without narrowing the 

 field too much. The eye-glass cannot be made very deep 

 without making it too thin in the centre. Even at present, it 

 would, perhaps, be difficult to make Galilean telescopes of 

 greater power than 32, which is, indeed, that which Galileo 

 obtained. 



On the 7th of January, 1610, Galileo discovered three of the 

 satellites of Jupiter ; on the 13th, the four satellites were ob- 

 served and recognized as satellites ; but it is not my object to 

 enter into that splendid strain of discoveries which illustrated the 

 name of Galileo, and which lately have been so well described. 



