E. M. NELSON ON EVOLUTION OF THE MICROSCOPE. 113 



considered, it will be seen that, because the illumination of trans- 

 parent objects with the mirror, and of opaque objects with the 

 mirror in conjunction with the Lieberkuhn, became so easy, there 

 was no need to turn the optic axis in any other direction than 

 that of one at right angles to the stage (though not necessarily, 

 as now, central to it). We find, therefore, that the mirror, 

 although applied in the first instance to a telescope mount, 

 became an important factor in determining the fixture of the 

 optic axis in a position at right angles to the stage. Undoubtedly 

 the mirror was the principal agent in extinguishing the hand 

 microscope of the type of Leeuwenhoek, Musschenbroek, Joblot, 

 Lieberkuhn. In illustration of this point it will be remembered 

 that in Part 1, Vol. 6, p. 354, it was stated that Culpeper 

 had mounted Wilson screw -barrel microscopes on a stand 

 (telescope mount), and had added a compound body and a 

 mirror to them. 



(In 1738 Dr. Smith alludes to mirror illumination in con- 

 nection with the Wilson screw barrel, and also to the addition 

 of a stand \Compleat System of Opticks, p. 401], but he 

 does not mention the attachment of a mirror to the stand 

 of a Wilson screw barrel, and from the way he treats the 

 subject it is probable that he was not acquainted with any 

 form of Wilson microscope mounted on a stand with a mirroi- 

 attached.) 



The precise date of these Culpeper- Wilson microscopes has not 

 been determined, but fortunately we have an excellent example 

 of the other kind figured by Baker in 1742.* Fig. 21 shows 

 a scroll form of mount on a circular wooden foot — a great 

 improvement over the complete telescope mount; but we see 

 the last remnant of a partial telescope mount, for the micro- 

 scope could be turned round on the pin CD laterally, so that 

 it might be pointed to the sky or to a candle flame. This 

 form of microscope, as made by Adams (see Adams' Micro- 

 graphia, first edition, 1746), which had the scroll made in 

 sections for the sake of portabihty, and which was mounted on 

 a square box foot, became very popular, and was still sold by 

 Jones in 1798. 



* Baker does not give the name of the maker of this microscope. They 

 were made by CufE, Adams, Mann and Ayscough, perhaps also by Culpeper 

 and Scarlet. 



JouRN. Q. M. C, Series II., No. 43. 8 



