242 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Reglet for Direct Reading in Microscopic Measurements. * — To 

 facilitate quick measurement with camera-lucida drawings, F. Guegueii 

 has contrived a simple apparatus such as every microscopist would he 

 able to make to suit his instrument. The Microscope having been first 

 slanted at a suitable inclination to the vertical, a rectangle is cut out of 

 & piece of celluloid, the longest side of this rectangle being equal to the 

 vertical distance separating the base of the micrometric screw from the 

 table on which the Microscope is placed. This transparent rectangle, 

 being placed upright on its narrow side in a plane parallel to the 

 plane of symmetry of the Microscope, is cut obliquely across the corner 

 by a line parallel to the axis of the instrument. The reglet thus 

 formed gives a means of always insuring the same slope of tube. 

 When the instrument has been thus inclined and provided with a 

 micrometer objective and a camera lucida at a variable angle, the 

 micrometric scale seen under the various magnifications employed, is 

 drawn successively on the table. For strong optical combinations a 

 tenth, or perhaps a fifth of a millimetre would be drawn : for weak 

 enlargements the entire scale would be drawn. Each of these traces 

 having been afterwards geometrically sub-divided into fractions, whose 

 smallest division would equal 1 //., it will only remain to counter-draw side 

 by side on the sheet of celluloid the various graduated scales (this can 

 be done by the aid of a graver or scalpel), and record their values. The 

 appropriate part of the celluloid sheet, when used for measurement, 

 would be superposed on the drawing obtained by the camera-lucida. 



Grimsehl's Liliput-projection Lantern.t — This instrument is made 

 by A. Kriiss, of Hamburg, to the design of Professor Grimsehl. Its 

 optical peculiarity is a short-focus illuminating lens. The light-source 

 is an electric arc lamp requiring a current of 1 • 5 amperes. The whole 

 arrangement is extremely compact, and being mounted on a pillar-stand 

 -can be raised or depressed at pleasure. 



A Micro-object Locater.J — S. E. Dowdy writes : "When showing 

 a mixed slide of objects under a low power to friends or to a class, the 

 necessity often crops up for locating a particular specimen which has 

 been picked out by the observer. There is an eye-piece on the market, 

 fitted with an index-needle, specially devised to overcome this difficulty ; 

 but it is expensive, and is very little, if any, more effective than the 

 contrivance which any working microscopist can make for himself. All 

 that is wanted is a circular piece of glass capable of fitting between the 

 eye-piece lenses, resting on the diaphragm usually to be found in the 

 eye-piece tube. This glass must be ruled off into small squares. If 

 one possesses a glazier's diamond, the glass can be cut and ruled at 

 home ; but any optician could get it done for a small sum. If, how- 

 ever, it is preferred to make it at home, and no diamond or glass-cutter 

 is available, here is an alternative method of manufacture. Get a cir- 

 cular glass, such as is used in phonograph reproducers, just the right 



* C.R. Soc. Biol, de Paris, lxiii. (1.07) pp. 117-18. 



t Central. Ztg. f. Opt. u. Mech., xxviii. (1907) pp. 307-8 (2 figs.). 



j English Mechanic, lxxxvi. (1908) pp. 5G4-5. 



