548 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
instruments, in which the coarse-adjustment is by sliding socket. It is 
intended to replace the popular revolver which is so inconvenient 
when any manipulation of the preparation has to be made on the stage. 
In fig. 59 the new adapter is represented 4/5 of its actual size. 
The adapter proper a is screwed in the ordinary way upon the body-tube 
instead of a system, while the objective to be used is provided with a 
connecting ring, the front edge of which fits exactly into a groove in the 
plate S. This plate is open on one side, in order to admit the neck of 
the connecting ring. A steel spring /, in the shape of a horse-shoe, 
screwed into the interior of the main-piece, serves to press the ring 
firmly into the groove. The plate S is attached to the main-piece a by 
four screws in such a way that an exact centering of the ring with the 
objective attached to it is insured. 
Paper for Cleaning the Lenses of Objectives and Oculars.*— The 
so-called Japanese filter-paper (the bibulous paper often used by dentists 
when filling teeth) is recommended for cleaning the lenses of oculars 
and objectives. It is said to be more satisfactory than cloth or chamois, 
because dust and sand are not present, and its bibulous character makes 
it very efficient in removing liquid or semiliquid substances. Use it for 
removing immersion-fluid from objectives, cloudiness or dirt from eye- 
pieces, glass slips, or thin glass. Water, glycerin, or other fluids can 
be removed. Another recommendation is its cheapness. 
(3) Illuminating- and other Apparatus. 
Use of Polarization-Photometer. t — Dr. S. Czapski discusses the 
arrangement of the sections in the polarization-photometer so as to obtain 
achromatism of the bounding line without achromatism of the calcite 
prism. He explains how necessary it is in the use of photometers of 
any kind that the faces of which the brightness is to be compared should 
have a sharply defined line of boundary. 
In polarization-photometers the usual arrangement consists in pro- 
ducing by double refraction two images a 0 a e and b 0 b e respectively, of 
two apertures a b situated at one end of the apparatus at a determined 
distance d apart. The magnitude of the double refraction bears such a 
relation to the distance of the apertures, that a 0 and b e are exactly adjacent, 
as seen in fig. 60. 
Since refraction is accompanied by dispersion, the edges of the images 
a 0 and b e have coloured seams, and since the dispersive power of calcite 
is essentially different for the ordinary and extraordinary ray, simul- 
taneous achromatism of both images is impossible. The most that can 
be done in this direction is to use, for the partial achromatism of the 
calcite prism, a flint glass with dispersive power lying between that of 
the ordinary and extraordinary ray in calcite, and thus to distribute 
the unavoidable chromatism uniformly over both images. In this case 
accordingly there remains a primary coloured seam on both boundary 
lines, which renders judgment of the brightness of the two fields difficult. 
The author proposes to remove this coloured seam by the very 
simple but ingenious device of arranging the apertures, not sym- 
* Araer. Mon. Micr. Journ., xiii. (1892) pp. 99-100. 
t Zeitsclir. f. lnstrumentenk., xii. (1892) pp. 161-2. 
