Dr. Moll on the Invention of Telescopes. 491 



However perfect we allow the instruments of Galileo to have 



been, we see no reason to doubt that the satellites could 



be seen with the instruments made in Holland. The Italian 



authors certainly assure us that the Dutch telescopes were of 



an inferior description ; but this assertion is wholly unsupported 



by proof. Indeed, we know nothing of these telescopes, except 



that they were long (tubi lonyi), and longer than sixteen 



inches * ; and it is not unrational to suppose that, with this 



length, they were equal to Galileo's telescopes. Admitting the 



length of the telescope to have been sixteen inches, and the 



negative focus of the concave eye-glass half an inch, the 



power of the telescope was 32, or equal to that of Galileo. 



The Professor Adrian Metiusf, brother of the co-inventor of 



the telescope, gives us some account of what could be seen 



with the telescopes then made in Holland. In a book printed 



in 1614, he says, ' During the day several planets are observed 



near the sun, which were unknown hitherto to all men, but 



which can only be seen with the glasses, which my brother, 



Jacob Adriaansz, invented six years ago (thus in 1608). 



These planets show themselves first in the eastern part of the 



sun, and from thence pass over the sun to the westward, in 



about ten days, as I observed several times, principally about 



sunrise and sunset. 



' With these same tubes some erratic stars or planets are 

 seen, which have their course round Jupiter ; but of these 

 nothing can be stated with certainty, unless my brother be 

 pleased to publish his telescopes, by means of which many 

 strange things will be brought to light, as well about the moon 

 as elsewhere. Yea, the observations of the stars may then be 

 made with much greater accuracy ; because, by means of 

 these telescopes, it will not only be possible to observe minutes, 

 but even seconds.' 



It does not appear from this quotation that the professor 

 himself observed the satellites ; nor does he even appear to be 

 aware of their number. His brother Jacob, perhaps, gave him 

 some incomplete information of the existence of the satellites. 



* De vero telescopii inventore, p. 30. 



t Adriani Metii, Institut. Astronom. et Geograph, Francq. 1614. Fonda- 

 mentale en groudelyche ouderuy singe, ibid 1614. Adriani Metii tract at us de 

 genuine usu utrusque globi, Francq. 1624. 4to. 



