G48 SUMMARY OF CURRENT RESEARCHES RELATING TO 



shown in figs. 150 and 151, which represent respectively fine and coarse 

 graduations. It will be observed that the ordinary strokes are replaced 

 by small squares placed cornerwise. The squares may be black or red. 

 Dr. Gebhardt speaks very favourably of his trials with these micrometers, 

 and describes which of Zeiss' oculars he found most suitable for them. 



TO at «* *" 



Fig. 150. 



Fig. 151. 



Apparatus for Measuring Micrometer Levels.* — M. Gouy, in his 

 investigations on the surface tensions of large drops, has found the 

 cathetometer unsuitable for small measurements, and has contrived a 

 micrometric method of measurement. His Microscope, provided with a 

 thread micrometer, rests by its three feet on a polished, plain, and 

 horizontal disk of glass. The Microscope is perfectly horizontal, and 

 can be raised and lowered. A closely divided vertical glass scale is so 

 arranged as to be also in the field of view. A point, A, on the micro- 

 meter can be thus identified on the scale, and the relation between A 

 and the scale zero be obtained. This operation repeated on other points 

 gives the differences of level desired. The author gives full practical 

 explanations, and states that the probable error of observation is only 

 about • 043/a. 



Greenman, M. T. — A New Laboratory Projection Apparatus. 



Anat. Record, No. 7, 1907. 

 Seibekt, W. & H. — Dnnkelfeldkondensor und Dunkelfeldblende. 



Zeit. f. angew. Mikr., xiv. (1908) p. 4. 



(4) Photomicrography. 



Interference Fringes produced by Photographs in Colours.f — 

 M. E. Rothe describes some observations on the above, sometimes called 

 Talbot's False Fringes. It is well known that an interferential photo- 

 graph illuminated by white light, and seen by reflection from the glass 

 side, exhibits fringes extending over the whole spectrum, from the red 

 to the violet. When the sensitive emulsion has been spread on a 

 perfectly horizontal glass the fringes are arranged almost parallel to the 

 spectral rays ; but if the gelatin layer varies in thickness, the fringes 

 are more or less inclined to the rays. These fringes can be more easily 

 studied in proofs obtained without mercurial mirror, for the colours are 



* Comptes Renclus, cxlvi. (1908) pp. 1191-3. 

 f Op. cit., cxlvii. (1908) pp. 43-5. 



