GALILEO'S 'OCCHIALE' 123 



linear amplification (as it is usually expressed now) would ha\e 

 been equal to something less than the cubic root of 50,000 that is, 

 about 36 and that is pretty fairly the relative size of a fly and 

 ;i hen. 



Aleandro's letter of May 24 (1624) does not state at what time 

 Galileo saw the telescope and explained the use of it, but another 

 letter of Faber's to Cesi, amongst the autograph letters in tin- 

 possession of I). B. Boncompagni, says (May 11): 'I was yesterday 

 evening at the house of our Signor Galileo, who lives near the 

 Madalena ; he gave the Cardinal di Zoller a magnificent eye-glass 

 for the Duke of Bavaria. I saw a fly which Signer Galileo him- 

 self showed me. I was astounded, and told Signor Galileo that he 

 was another creator, in that he shows things that until now we 

 did not know had been created.' So that even on May 10, 1624, 

 Galileo had not only seen the telescope of Drebbel, and explained 

 the use of it, but had made one himself and sent it to the Duke of 

 Bavaria. 



We lack documents to show how this microscope of Galileo was 

 made, that is, whether it had two convergent lenses like those of 

 Drebbel. A letter of .Peiresc of March 3, 1624, says that 'the 

 effect of the glass is to show the object upside down . . . and so 

 that the real natural motion of the animalcule, which, for example, 

 goes from east to west, seems to go contrariwise, that is, from west 

 to east,' or whether it was not rather composed of a convex and a 

 concave lens, like that made earlier by him, and used in 1610, and 

 then almost forgotten for fourteen years. 



It is, however, very probable that this last was the one in 

 question, for Peiresc, answering Aleandro on July 1, 1624, wrote : 

 'But the occIiniJ,' mentioned by Signor Galileo, which makes flies 

 like hens, is of his own invention, of which he made also a copy 

 for Archduke Albert of pious memory, which used to be placed on 

 the ground, where a fly would be seen the size of a hen, and the 

 instrument was of no greater height than an ordinary dining-room 

 table.' Which description answers far better to a Dutch tele- 

 scope used as a microscope, in the same way exactly as Galileo 

 had used it, rather than to a microscope with two convex 

 lenses. 



One cannot 'find any further particulars concerning Galileo's 

 occhialini (so he had christened them in the year 1624), either in 

 Bartholomew Imperial's letter of September 5, 1624, in which he 

 thanks Galileo for having given him one in every way perfect, or in 

 that of Galileo to Cesi of September 23, 1624, accompanying the 

 gift of an occh latino, or in Federico Cesi's answer of October 26, or 

 in a letter of Bartholomeo Balbi to Galileo of October 25, 1624, 

 which speaks of the longing with which Balbi is awaiting 'the little 

 occhiale of the new invention,' or in that of Galileo to Cesar Marsili 

 of December 17 in the same year, in which Galileo says to the 

 learned Bolognese ' that he would have sent him an owliniVmo to 

 see close the smallest things, but the instrument maker, who is 

 making the tube, has not yet finished it.' This, however, is how 

 Galileo speaks of it in his letter to Federico Cesi, written from 



