148 THE MICROSCOPE. Oct. 



He says (page 234) : " In regard to the lighting, and 

 some other requisites of illumination, an Argand burner 

 lamp is used, a bull's-eye condenser being adjusted as 

 near as possible to the flame, and a large image of the 

 flame projected so as to fall on the concave face of the 

 mirror." He not only uses a convex flame-surface, but 

 he endeavors to condense the light on the concave mir- 

 ror, when the source of that light is not in the focus of 

 the bull's-eye, since he puts the bull's-eye "as near as 

 possible to the flame." This might not be so bad, but 

 "To the sub-stage," he continues, "an achromatic con- 

 denser is adapted, and when the light is properly cen- 

 tered in the field, the result will be a dazzling light. But 

 in order to guarantee the successful view of the various 

 phenomena, it is necessary to have at hand a glass slip, 

 or a smaller piece of emerald or grass-green colored 

 glass (blue will not answer). This slip must be placed 

 on top of the condenser, or the slide containing the liv- 

 ing diatoms must rest directly upon the green glass slip." 



If this again means what it says, then Mr. Cunning- 

 ham uses the concave mirror with the achromatic con- 

 denser, having the bull's-eye placed between the mirror 

 and the light but not focussed, and the condenser itself 

 out of focus, whether within or without it is hardly pos- 

 sible to guess, but probably w^ithout ; and to " make con- 

 fusion worse confounded," he inverts a small-angled, 

 half-inch objective and uses it as an eye-piece. When 

 these things have been accomplished, Mr. Cunningham 

 gravely describes his observations, and not only expects 

 the general reader of this Journal to treat his paper as 

 something more thnn an "American joke," but he seems 

 to want expert microscopists and biologists, learned dia- 

 tomists and naturalists, to accept the statement that he 

 has proved the motile diatoms to be animals, and proved 

 it by the optical methods, or rather by the absence of 

 optical methods, which he so explicitly details. 



