294) REINICKE, " Z. NEUERN MIKROSKOPIE." 



The distance between a b, or c d, corresponds to the 

 breadth of the glass plates, or = 12mm., whilst the Avidth of 

 the other two sides is equal to the length of the glass plates 

 when placed at the proper angle, as indicated in the line /, m. 

 The breadth b c,that is to say, the distance between the sides b i, 

 and c b, must, in other words, be such that when a glass plate 

 18mm. long, is placed between them, it should form, with 

 the axis of the tube, the angle of 35° 25", or very nearly 

 so. This distance can, of course, be readily found by raising 

 a line I m, from the point x, at an angle of 35° 25" with b i, 

 measuring off on / m, the length of the glass plate, slip, and 

 drawing at that point another line c h, parallel with b i. 

 Thus is obtained the width of b c, with which d e'\^ made to 

 correspond. 



The cardboard is now to be cut nearly through, in the di- 

 rection of the lines bi, c li, and dg^ so that the four portions 

 can be readily bent upon each other. The inner side of the 

 paper should be painted black, or pasted over with black 

 paper, and when all is dry the four sides are brought round, 

 and the edges a k, and e f, joined with a little gum. But 

 before the sides are joined, a narrow slip of the same, or of 

 thinner cardboard, should be gummed across either a, b, i, k, 

 or c, d, g, b, a short distance fi'om one end, as at /, n. The 

 tube being thus constructed, one of the glass slips is dropped 

 in it, so that one end of the slip rests upon the little ledge I n, 

 the other, of course, abutting upon the opposite side of the 

 tube, at the proper angle. All that now remains is to drop 

 in the requisite number of glass slips, one upon another, and 

 to see that they come into close and parallel contact with 

 each other. When the last glass slip has been placed, a 

 second slip of cardboard, similar to / n, should be glued to 

 the wall of the tube, immediately above the upper edge of the 

 slip. The whole set will thus be secured from displacement. 



The number of glass slips to be employed, varies according 

 to circumstances. The greater the number, the more com- 

 pletely is the light polarized, but at the same time, its quan- 

 tity is diminished, especially when the glass is not absolutely 

 colorless. Five plates afford scarcely any polarization, but 

 witb ten a considerable effect is obvious in the change between 

 the light and dark fields. Fifteen plates show indications of 

 the cross in potato-starch, which is rendered very distinct by 

 twenty, and is perfectly sharp and well defined by twenty-five 

 slips ; whilst at the same time the field, when two polarizers 

 are at right angles, is almost perfectly dark. Here it is 

 generally advisable to stop. But with perfectly colourless 

 glass as many as thirty slips may be inserted, but beyond 



