HISTORY OP THE MICROSCOPE. 9 



similar to that which Mr. Martin published as new, in his 

 Mici-ographia 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. 



A short time before this, Sir Isaac Newton having dis- 

 covered his celebrated theory of light and colours, was led 

 to improve the telescope, and apply his principles most 

 successfully to the construction of a compound reflecting 

 microscope. On the 6th of February, 1672, he communi- 

 cated to the Royal Society his " design of a microscope by 

 reflection." It consisted of a concave spherical speculum 

 of metal, and an eye-glass which magnified the reflected 

 image of any object placed between them in the conjugate 

 focus of the speculum. He also pointed out the proper 

 mode of illuminating objects by artificial light, as he 

 describes it, " of any convenient colour not too much 

 compounded," mono-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 communicated to the public. The vast magnifying 

 power obtained by this instrument, the colossal grandeur 

 with which it exhibited the " minutiae of nature." the plea- 

 sure 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 polype. The discovery of the wonderful properties of 

 this little animal, together with the works of Mr. Trembley, 



