xni, c,4 Shaw: Microtechnical Methods 243 



by the use of fragments of cover glasses. Pieces of capillary 

 glass rods serve this purpose well. Ordinary glass rods are 

 heated to softness in a flame and drawn out to suitable thinness. 

 As they then taper more or less it is well to pass the drawn 

 rods through the jaws of a cover-glass tester, of the type manu- 

 factured by Zeiss, and break them at points corresponding to 

 the limitations selected for a series of grades according to size. 

 I keep the graded pieces of rod in marked watch glasses or vials 

 and break them into short lengths for use. Four short pieces 

 are distributed on the slide in the Venetian turpentine before 

 the cover is added. A light clip is used to make the cover settle 

 down on the rods. One advantage of using rods instead of 

 bits of cover-glass is that the rods, being approximately cylin- 

 drical, may have their thickness determined, at any time after 

 being mounted, by the use of the ocular micrometer. 



AUTOGRAPHIC RECORDS ON MICROGRAPH IC NEGATIVES 



These may be made by a device so simple that it seems prob- 

 able that it has already been employed. I have used it for 

 numbering negatives, but it is suitable for any autographic re- 

 cord, which it may be desirable to make on a micrographic or 

 other photographic plate in the laboratory, and might be adapted 

 to service with a plate camera in the field. The data are 

 written with black drawing ink on a piece or pieces of trans- 

 parent celluloid. Kodoid plates furnished the celluloid used by 

 me. For serial numbers the labels were prepared in advance. 

 After all adjustments have been made preliminary to insertion 

 of the plateholder, the celluloid label is attached by bits of 

 adhesive tape to the metallic diaphragm close to the focal plane 

 of the camera, in a part of the field selected for the purpose. 

 Its location may be verified by making another inspection of 

 the image on the ground glass before inserting the plate holder 

 for the exposure. 



A METHOD OF RECORDING MAGNIFICATION ON MICROGRAPHIC 



NEGATIVES 



It is a simple matter to photograph the image of a slide- 

 micrometer scale on a negative beside the image of any micro- 

 scopic object so that the scale and object appear side by side on 

 the photographic positive and any reproduction. The advantage 

 of this method of indicating the scale of magnification over that 

 in which the scale is drawn on the finished print is obvious. 



For this purpose one side of the circular camera field is 

 blocked out by a screen attached to the metallic diaphragm, 



