312 THE AMERICAN" MONTHLY |Nov 



pond life, etc., ordinary i-plate lenses of the rapid sym- 

 metrical type or the modern anastigmats can be advan- 

 tageously used, and by employing the 35mm. or 20mm. 

 Zeiss Planar lenses an infinite amount of low or even 

 medium-power work can be done, for I have found that 

 the ordinary spiral rack and pinion attached to the camera 

 is sufficiently delicate for focussing with these powers. 



When, however, medium or high-power work is under- 

 taken, and especially when it is thought desirable to em- 

 ploy apochromatic objectives in conjunction with com- 

 pensating or projection eyepieces, a special form of ac- 

 cessory apparatus is essential. Messrs. Watson and Sons 

 have constructed this from my designs at a most season- 

 able cost, and, like all the productions of that firm, the 

 workmanship is throughout excellent. It consists chiefly 

 of a body tube of Continental length, supported upon a 

 metal base, with spiral rack-and-pinion coarse adjust- 

 ment, and a delicate side-lever fine adjustment, with its 

 milled head conveniently placed upon the right side of 

 the instrument. Its optical axis is only 2§ in. high. 



When this apparatus is in use, the stage is pushed up 

 to a convenient distance from the objective employed, and 

 clamped. The object is then focussed in the usual way, 

 the camera front racked up so that its light-tight cap is 

 inserted within another larger cap upon the body tube, 

 which may or may not carry an eyepiece, and the expo- 

 sure made. 



It will be seen that the limb and body tube of the mi- 

 croscope is not attached to the stage, so that the former 

 can be removed and dispensed with when only low-power 

 work is undertaken. With this small and compact appa- 

 ratus it is possible to photograph any object varying in 

 size from, say, the wing of a large dragon-fly to a bacte- 

 rium or bacillus. 



By keeping the axis of the optical system low — only 2| in- 

 from the base — the size of the rest of the apparatus is nee- 



