DIVINTS o IMPOUND MICKOSCOPE 



129 



of its employment, which are at once interesting and instruc- 

 tive ; for they show quite clearly that it was not employed by him 

 to correct the spherical aberration of the 

 eye-lens, but merely to increase the size of 

 the field of view. He tells us that he used 

 it ' only when he had occasion to see much 

 of an object at once. . . . But whenever 

 I had occasion to examine the sinal} parts 

 of a body more accurately I took out the 

 middle glass (field-lens) and only made use 

 of one eye-glass with the object-glass.' 



Fig. 94 is a reproduction of the original 

 drawing, and the general design appears 

 to be claimed by Hooke. There is a ball- 

 and-socket movement to the body, of 

 which he writes : ' On the end of this arm 

 (I), which slides on the pillar C C) was 

 a small ball fitted into a kind of socket 

 F, made in the side of the brass ring < >. 

 through which the small end of the tube 

 was screwed, by means of which contri- 

 vance I could place and fix the tube in 

 whatsoever posture I desired (which for 

 many observations was exceedingly neces- 

 sary), and adjusted it most exactly to any 

 object.' 



It need hardly be remarked that, useful 

 as the ball-and-socket joint is for many 

 purposes in microscopy, it is not advan- 

 tageously employed in this instrument. 



Hooke devised the powerful illuminat- 

 ing arrangement seen in the figure, and 

 employed a stage for objects based on a 

 practical knowledge of what was required. 

 He described a useful method of estimat- 

 ing magnifying power, and was an in- 

 dustrious, wide, and thoroughly practical 

 ol>.>prver. But he worked without a 

 mirror, and the screw-focussing arrange- 

 ment seen in the drawing must have been 

 as troublesome as it was faulty. But as a 

 microscopist, Hooke gained a European 

 fame, and gave a powerful stimulus to 

 microscopy in England. 



In 1668 a description was published 

 in the * Giornale dei Letterati ' of a com- 

 pound microscope by Eustachio Divini, 

 which Fabri had previously commended. 

 It was stated to be about 16^ inches 

 high, and adjustable to four different 

 lengths by draw-tubes, giving a range of 



FIG. 95. Divini's compound 

 microscope (1668). 



