9(i SUMMARY OF CURRENT RESEARCHES RELATING TO 



for low-power photomicrography. The device consists of ;i sliding plate 

 screwed to carry the objective, and laterally displaceable by means of a 

 small rack-and-pinion (rig. 4). For several reasons this method is more 

 convenient than moving the object, as the illumination is unaltered 

 and the shadows fall on their right place. The apparatus can lie used 

 only on Microscopes with a large body-tube, but a half-plate camera and 

 a Microscope fitted with the Zeiss sliding objective changers are all that 

 is necessary for high-power work, as the lateral screw of these changers 

 moves the objective adequately and efficiently. 



Arc Lamps for Projection.* — H. P. Gage has, with the help of the 

 General Electric Company at Schenectady, made an exhaustive series of 

 investigations on the above subject. These investigations were suggested 

 by, and supplementary to, certain preliminary investigations at Cornell 

 University. They dealt with direct and alternating currents as applied 

 to the three ordinary types of projection lamps, viz. with inclined carbons, 

 with electrodes at right angles, with converging electrodes. Full descrip- 

 tions, with diagrams, are given of the experiments and results. The 

 author concludes that a direct current obtained from a mercury-arc 

 rectifier gives almost as much light as a direct current from a generator. 

 In every case direct current gives much more light for equal current 

 values than does alternating current. He is of opinion that evidently 

 the power drawn from the line depends upon the power consumed at 

 the arc and the efficiency of the " ballast " or transforming device. Of 

 the devices tested the rectifier was the most efficient, and the least 

 efficient was a resister used with alternating current. 



Improvement in the Illumination of Objects observed with the 

 Binocular Microscope.t — C. Cepede, in the course of his botanical and 

 zoological researches with the binocular Microscope, has found rather 

 serious inconvenience arise from the formation of a shadow zone in the 

 part of the object turned towards the observer. This shadow is a 

 hindrance, by its depth, to the minute morphological and anatomical 

 study of all this part of the object. The author has overcome the 

 difficulty by illuminating the part in question by the help of a concave 

 mirror, which may be applied in three ways. 



First Arrangement. — In this case, midway between the holes ad- 

 mitting the spring-clips, the stage is pierced by a similar hole for the 

 admission of a cylindrical screw-piece, resembling those bearing the 

 clips. To this screw-piece is attached a brass or nickel rod, bent at 

 right angles, and carrying a mirror-holder at its further extremity. The 

 mirror is fixed by help of screws, so that it has movement in two direc- 

 tions. The whole arrangement thus has a triple articulation, and can 

 be directed as desired. 



Second and Third Arrangements. — In these the screw which fixes the 

 arm of the Microscope to the stage is used for screwing the mirror- 

 holder, which may be fastened either to the upper part of the arm 

 (second arrangement) or to its lower part (third arrangement). The 

 mirror-carrier itself is substantially the same as in the first arrangement. 



* Electrical World, Oct. 13, 1910 ; and as a separate pamphlet, 5 pp. (9 figs.). 

 t Comptes Eendus, cli. (1910) pp. 948-9. 



