262 SUMMARY OF CUERENT RESEARCHES RELATING TO 



Dr. Dippel says that lie has thoroughly tested the camera with 

 very delicate drawings, and has found it of excellent service, and 

 he considers it is to be preferred over all those forms for drawing on 

 a horizontal surface in which the microscopical image is seen after 

 several, reflections, and the pencil direct. 



Curtis's Camera Lucida Drawing Arrangement.*— Mr. Bulloch's 



new " Congress " stand has an arrangement for drawing, suggested 

 by Dr. L. Curtis, " which is designed to do away with some of the 

 difficulties attending the use of the ordinary camera lucida. A little 

 table is fastened to the limb by milled-head screws ; paper is placed 

 upon this for drawing. One of Hartnack's right-angled camera 

 lucidas is used. Drawing can be done in any position of the 

 Microscope. There is hardly more preparation required for this 

 than would be required to change an eye-piece. The comfort of this 

 arrangement, when one is doing work which requires much drawing 

 while observation is going on, needs to be experienced to be 

 appreciated." 



Drawing on Gelatine with the Camera Lucida.t — M. Creteur 

 uses a metallic point for drawing objects with a camera lucida, the 

 drawing being made not on paper, but on a sheet of gelatine laid on a 

 dark ground. The shining point is always visible, and is claimed to 

 provide a remedy for the indistinctness of the point of the pencil, which 

 is the chief difficulty experienced in drawing with the camera by the 

 ordinary method. The drawing can also be readily transferred to 

 stone. 



It is questionable whether the advantage gained through the 

 greater distinctness of the drawing-point is not more than counter- 

 balanced by the disadvantage of not being able to draw on paper. As 

 the particular benefit claimed appears to rest upon the shining 

 point, that could be obtained without great difficulty with an ordinary 

 pencil. 



Iris-Diaphragm for varying the Aperture of Objectives. — In 

 1869, Dr. Eoyston-Pigott applied an Iris-diaphragm behind the 

 objective for reducing the aperture of objectives, in support of the 

 view which he was then advocating that wide-aperture objectives 

 produced confused images. 



The editor of the ' Northern Microscopist ' has recently suggested 

 the use of such a diaphragm to enable penetration to be obtained 

 with wide-angled objectives of different apertures. Fig. 48 is a side 

 view of the apparatus, as made by Mr. C. Collins, and Fig. 49 a front 

 view. The upper end in the former figure screws into the microscope- 

 tube, while the lower receives the objective. The diaphragm is 

 opened or shut by sliding the lever projecting at the side. The 

 partial closing of the diaphragm does not, of course, contract the 

 Jield, but diminishes its brightness by obstructing the passage of a 

 greater or less part of the cone of rays. 



* Amer. Mon. Micr. Journ., iii. (1882) p. 13. 

 t Bull. Acad. R. Med. Belg., 1880, p. 617. 



