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



have probably influenced the design of Powell's No. 1. We 

 say probably, because it is possible that Powell's No. 1, or any 

 other form of microscope or apparatus, might have been 

 designed by an inventor wholly unacquainted with any pre- 

 ceding form, though in the absence of any evidence to the con- 

 trary such a hypothesis would be highly improbable. 



Those parts of this paper which treat of old microscopes are 

 not intended to be a history of the microscope ; many interest- 

 ing old forms will not even be mentioned. For the most part 

 attention will be drawn to only those instruments that have 

 been rungs in the ladder of evolution. 



To begin, then, neither the name of the inventor nor the date 

 of the first compound microscope has been with certainty 

 «_ «* determined. There is an extensive literature on 

 the subject, and the conclusion arrived at is that 

 the first microscope was probably made by Jansen, 

 a spectacle maker, of Middelburg, in Holland, about 

 the year 1660. An old microscope, supposed to be 

 a Jansen, was exhibited at the loan collection of 

 scientific instruments at South Kensington in 1876 

 (catalogue No. 3,510), the date of it given in the 

 catalogue being 1590. This instrument had neither 

 stand, object-holder, nor stage ; the only mechanical 

 movement with which it was furnished was a draw 

 tube for separating the two convex lenses which 

 formed the optical part of the instrument (Fig. 1). 

 The next step is to be found in a drawing of a simple micro- 

 scope by Descartes in his "Dioptrique" in 1637. This shows 

 a piano convex lens placed at the vertex of a concave mirror; 

 in short it is an instrument now known as a Lieberkuhn. It 

 is curious to note that while Descartes is very particular 

 about the parabolic curves of his mirrors and the hyperbolic 

 curves of his lenses the figures show the lenses turned the 



wrong way, which would cause the 

 spherical aberration to be increased 

 four-fold. Now as the difference 

 between the aberrations arising 

 from the spherical and hyperbolic 

 curves is for the purposes under 

 consideration insignificant, the 



Fig.i. 



