HISTORY bF THE MICROSCOPE. 7 



by which means the glass takes in more of an object, the field is larger, 

 the extremities of it less curved, and the magnifying power greater. 

 The tube in which the glasses were enclosed was as large as a man's 

 leg, and the eye-glasses as broad as the palm of the hand. It had four 

 several lengths : when shut up was 16 inches long, and magnified the 

 diameter of an object 41 times, at the second length 90, at the third 

 length 111, and at the fourth length 143 times." It does not appear 

 that Divini varied the object-glasses. 



''^ Philip Bonnani published an account of his two microscopes in 

 1698. Both were compound. The first was similar to that which 

 Mr. Martin published as new, in his Jficrographia Nova, in 1712. His 

 second was like the former, composed of three glasses, one for the eye, 

 a middle glass, and an object lens ; they were mounted in a cylindrical 

 tube, which was placed in a horizontal position ; behind the stage was 

 a small tube with a convex lens at each end ; beyond this was a lamp ; 

 the whole capable of various adjustments, and regulated by a pinion 

 and rack. The small tube was used to condense the light on to the 

 object, and spread it uniformly over, according to its nature, and the 

 magnifying power that was used. 



^,^, A short time before this, Sir Isaac Newton having discovered his 

 celebrated theory of light and colours, was led to improve the telescope; 

 and in 1672 he is said to have applied his principles most successfully 

 to the construction of a compound reflecting microscope. He also 

 pointed out the proper mode of illuminating objects by artificial light, 

 as he describes it, " of any cqnvenient^colour not^too much compounded, 

 «M>wo-chromatic." We find other two plans of this kind; the first that 

 of Dr. Robert Barker, and the second that of Dr. Smith. In the latter 

 there were two reflecting mirrors, one concave, and the other convex : 

 the image was viewed by a lens. This microscope, though far from 

 being executed in the best manner, performed, says Dr. Smith, very 

 well, so that he did not doubt it would have excelled others, had it 

 been properly finished. 



In 1738, Lieberkuhn's invention of the solar microscope was com- 

 municated to the public. The vast magnifying powen obtained by this 

 instrument, the colossal grandeur with which it exhibited the " minutiae 

 of nature," the pleasure which arose from being able to display the 

 same object to a number of observers at the same time, by affording a 

 new source of rational amusement, increased the number of microscopic 

 observers, who were further stimulated to the same pursuits by Mr. 

 Trembley's famous discovery of the polyp. The discovery of the 

 wonderful properties of this little animal, together with the works of 



