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XLVII. The Dichrooscope. By H. W. Dove*. 



[With a Plate.J 



THE apparatus to which I have given the above name is in- 

 tended for the following purposes : — 



1. To represent interferences, and spectra in different-coloured 

 lights, both separately and combined. 



2. To imitate the phenomena of dichroism both in the case 

 in which the dichroitic crystals are viewed through a double- 

 refracting arrangement, as, for example, Haidinger's dichroitic 

 lens, and also in the case of the phenomena produced when the 

 dichroitic crystals themselves are used as analysers in a polarizing 

 arrangement. 



3. To combine elliptically, circularly, and rectilinearly polar- 

 ized and unpolarized light, not in such a manner that the one 

 is produced by the polarizing, and the other by the analysing 

 arrangement, but so that they traverse the doubly refracting 

 media simultaneously, and are then submitted to any analysing 

 arrangement. 



a b, fig. 1, Plate IV. is the three-sided brass prism of my 

 polarizing apparatus {Farbenlehre, page 202), moveable in a 

 brass case on an ordinary telescope-stand, in horizontal and 

 vertical directions. At one end there is the lens with the polar- 

 izing mirror c d, and at the other end at a the analysing Nicol 

 with the ocular, hegfis the dichrooscope, which can be placed 

 in one of the ordinary slides which carry the other arrange- 

 ments, in which case these other arrangements (the polarizing 

 Nicol and the circular-polarizing mica plate) may be placed on 

 one side. 



The dichrooscope is a four-sided brass box 81 millims. long, 

 75 millirns. high, and 70 millims. broad. The posterior side of the 

 box represented in the figure is closed, and in the middle of this 

 side there is a cylindrical piece in which a rod is inserted. This 

 rod is attached either to a piece of glass ef, or to a moveable glass 

 disc, which can thus be exchanged for one another. The piece 

 of glass or the disc are turned by means of a knob which pro- 

 jects from the outside of the box, after the end of the rod 

 which reaches out of the cylindrical piece has been tight- 

 ened by a screw, but not so as to prevent rotation. In the open 

 sides of the box hf and fg coloured glasses can be inserted, 

 while h e, when other slides are not used, is destined to receive 

 cooled glasses or crystals, or a large rotating circular-polarizing 

 plate of mica. The sides hf and gf can be closed by slides ; and 

 slides can be placed in he which have a longitudinal slit for prism- 



* Translated from Poggendorff's Annalcn, vol. ex. p. 265. 



