1881.] 



MICKOSCOPICAL JOUKNAL. 



175 



the former, to act upon the conclu- 

 sions thus attained. 



Another suggestion we have in 

 mind relates to the polariscope. This 

 useful accessory is not readily applied 

 to any of the stands made in this 

 country, except those specially de- 

 signed for mineralogical work. Some 

 ingenious arrangement should be de- 

 vised whereby the polarizer can be 

 swung into place and removed as 

 readily as objectives can be changed 

 by a double nose-piece, and the ana- 

 lyzer should be arranged for equal 

 convenience of application. 

 o 



Zeiss's Camera Lucida. — 

 Through the courtesy of Mr. Fr. 

 Emmerich, of this city, who has lately 

 received a number of articles from 

 Mr. Zeiss, among which, in a ^-inch 

 homogeneous immersion objective, 

 we have been enabled to make use 

 of the two-prism camera lucida 

 by Zeiss ; as this accessory is 

 almost unknown in this country, an 

 account of its performance may be 

 of interest. 



The instrument consists of two 

 prisms so arranged that when placed 

 over the eye-piece, with the micro- 

 scope vertical, an image of a portion 

 of the surface of the work-table is 

 projected into the field of view, so as 

 to be distinctly seen together with 

 the object on the stage. The drawing 

 paper may be placed either on one 

 side of the microscope or behind it, 

 as may be most convenient, but if on 

 the side, the paper should be in- 

 clined about 15° or 20° ; if behind 

 the microscope, the stand itself may 

 be inclined instead ; and this we find 

 to be the more convenient and sim- 

 pler plan. We have been very much 

 pleased at the ease with which the 

 pencil-point can be seen with this 

 camera lucida. In this respect it is 

 superior to any other that we have 

 tried, although our experience in this 

 respect has been rather limited. 

 Moreover, it is much less trouble- 

 some to work with than the Wollas- 

 ton prism, which is the one in most 



common use in this country. It 

 meets one great desideratum in a 

 camera lucida, viz., that it can be in- 

 stantly applied while the microscope 

 is vertical or at a slight inclination, 

 without any change of conditions, 

 such as are necessary with the Wol- 

 laston form, which not only cause 

 trouble, but also much loss of time 

 and often the loss of the object. Our 

 experience, after finding a beautiful 

 desmid, for example, which we de- 

 sired to portray on paper with the 

 WoUaston prism, has at times been 

 very trying. First, the slide must be 

 secured in place, then the microscope 

 must be elevated to a suitable height 

 on a pile of books or boxes, and a 

 large space on the table cleared. 

 Then, after arranging the tube hori- 

 zontally, the object must be illumin- 

 ated and focussed — probably it must 

 be searched for again — and then we 

 are about ready to draw. How 

 much simpler it is to merely adjust 

 the Zeiss prism over the eye-piece, 

 place the paper on the table, adjust 

 the light and proceed with the 

 drawing 



We have given considerable space 

 to this subject, because we believe 

 that if a good camera lucida, which 

 could be thus readily used, were in 

 the hands of our microscopists, many 

 more drawings would be made, and 

 habits of close observation would be 

 thereby cultivated. We can heartily, 

 and without hesitation, recommend 

 Mr. Zeiss's form, and hereafter we 

 propose to use it ourselves. 



The Holman Compressorium.— 

 We have received from the manu- 

 facturers, Messrs. J. W. Sidle & Co., 

 one of their new Holman compress- 

 oriums, and after a fair trial we can 

 confidently recommend it as a very 

 useful accessory for the microscopist, 

 especially in the study of minute 

 animals in water. It seems to be dis- 

 proportionately large, but probably 

 the makers have good reasons for 

 making it so. The cover is of mica 

 and is, therefore, not easily broken. 



