THE MICROSCOPE. 5 



Hartsoeker was bom. Hooke describes exceedingly well the 

 process of making globule lenses, which is as follows: — "If you 

 take a clear piece of Venice glass, and, in a lamp, draw it out 

 into fine threads, and then hold the ends of these threads in 

 the flame, until they melt, they will run into a small round 

 globule or drop, which will hang to the end of the thread; 

 having made a number of these, they are all to be stuck upon 

 the end of a stick with a little sealing-wax, with the threads 

 standing uppermost ; these ends are to be ground off first on a 

 whetstone, and then polished on a metal plate with tripoli. 

 The lenses thus finished, if placed against a small hole made 

 in a thin piece of metal, and fixed there with wax, will both 

 magnify and make some objects more distinct than any of the 

 great microscopes can do." 



The optical part of the microscope of Hooke consisted of a 

 small object-glass, a field-glass, and an eye-glass; when he 

 wished to examine the parts of an object more accurately, he 

 removed the middle or field-glass, and by that means he 

 states he obtained more light and better definition. The 

 compound body was of the shape represented by fig. 1, and 

 when shut up was seven inches in length, and three inches in? 

 diameter, but was capable of being drawn out like a telescope;, 

 being supplied with four tubes or slides ; it was also capable 

 of being inclined at any angle by means of a ball and socket 

 joint, as represented by fig. 1. Coeval with Hooke were 

 Eustachio Divini, of Rome, and S. Campani, of Bologna, the 

 former of whom, in the year 1668, published, in the Philo- 

 sophical Transactions, an account of his microscope, which 

 consisted of an object-glass and field-glass, like that of Hooke, 

 but, instead of a double convex eye-glass, he substituted two 

 planoconvex lenses, which touched each other in the middle 

 of their convex surfaces ; by this arrangement a flat field of 

 view was obtained, at the same time with a considerable 

 amount of magnifying power. It is said,* that the compound 

 body of this instrument, when shut up, was sixteen inches 

 long, and as large in circumference as a man's thigh, and that 

 the eye-glass was equal in size to the palm of the hand ; ita 

 * Chevalier Des Microscopes et de leur usage, p. 15. 



