724 SUMMARY OF CUREENT RESEARCHES RELATING TO 



Althougli there is much disparity in the opinions, it is only the 

 older observers who are really in competition for the honour of the 

 discovery ; that is, Joblot and the Royal Society, but it does not appear 

 clearly from the known records which of the two preceded the other. 



The ' Philosophical Transactions ' do not speak of any such obser- 

 vation, but, consulting the ' History of the Royal Society,' written 

 by Birch, in which are found described with great care almost all 

 the experiments, letters, communications, and discussions which the 

 English savants did not think worthy to appear in the volumes of 

 their ' Transactions,' we may read there in the second volume the 

 following passages : — 



Under the date of the 11th of February (Thursday), 166f (count- 

 ing ah incarnatione, and according to the Julian calendar) : ' The 

 operator was ordered to speak to Mr. Hooke, that the great Microscope 

 of Mr. Christopher Cock's making be brought to the Society at the 

 next meeting.' And the 18th of February 166| (Thursday), 'Mr. 

 Christoj)her Cock produced a Microscope which he said he had made 

 for the Society if they liked it, with five glasses, of which the four 

 eye-glasses were plano-convex, two and two so put together as to 

 touch one another in a point of the convex surface. Various observa- 

 tions being made therewith, it appeared to do very well, but there 

 being a guinea put in it and looked upon, some of the members saw 

 the image depressed, others embossed. The workman referred him- 

 self to the Society for the price of this Microscope, and the Society 

 referred it to the Council.' 



Then the Council decides on the 22nd of February (Monday) : 

 ' That the Treasurer pay to Mr. Christopher Cock 81. for a large 

 Microscope made by him for the Society.' It does not appear that 

 the Society or any of its members made any further investigation 

 after this into the singular illusion discovered on the 18th (28th ac- 

 cording to Gregorian style) of February 1669, although the 202 

 Italian lire (8/.) paid for the Microscope which had demonstrated it 

 attest the importance attributed to Mr. Christopher Cock's instrument. 

 The date of the first observation of the English academicians being 

 thus established, Joblot's priority disappears, unless it is wished to 

 uphold it on the ground that the discovery remained unpublished 

 in the records of the Royal Society until the time of its publication 

 by Birch (1756). 



In any case, even recognizing the priority of the English, we 

 are able justly to claim for an Italian countryman of ours the credit, 

 not only of having anticipated the Royal Society in the discovery 

 of the curious illusion, but of having forestalled those physicists 

 who subsequently endeavoured to explain it. Eustachio Divini, 

 of San Severino (the ancient Septempeda), on the frontier, was the 

 most skilled manufacturer of lenses and glasses of all kinds of his 

 time, and in the year 1 649 had conceived the idea of placing in a 

 telescope which he possessed, some fine threads crossed, substituting 

 a convex ocular lens for the concave ocular used by Lippersheim and 

 Galileo, in order to see the network and thus sketch with ease the 

 image of the moon which, with all its markings, was depicted uj)on it. 



