ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



285 



Fig. 34. 



Zentmayer's Nose-piece.* — This (fig. 34) is yet another of the 

 nose-pieces for rapidly changing objectives, so many of which have 

 been brought out during the last few months. 



Mr. Zentmayer's plan consists simply in 

 the adoption of Mr. Nelson's form of adapter 

 (see vol. ii. (1882) p. 858) with the inner 

 screw-thread filed smooth in two opposite 

 segments, but in place of altering the thread 

 of the objective itself, he puts on it a separate 

 collar, the inner thread of which is entire, but 

 the outer thread filed smooth in two places 

 in a similar way to that of the adapter. 



Mr. Zentmayer thought it useless to adopt 

 the original plan, " unless all the prominent 

 manufacturers would agree to cut the screw- 

 threads of objectives and nut in the same rela- 

 tion," which would be diflftcult to establish ; 

 but "by means of the collar he can manu- 

 facture a nose-piece and collar for any objec- 

 tive without having either at hand.'' 



Tornebohm's Universal Stage Indicator. t— A. E. Tornebohm 

 describes his arrangement as follows : — " Every petrological Micro- 

 scope is now, as a rule, provided with a scale, or other arrangement 

 on the stage, whereby we can readily find again any particular point 

 in a preparation which it is desired to mark. According to the methods 

 hitherto used, however, the contrivance which gives the position of a 

 point in the preparation, is only available for a given Microscope, or 

 at most for the Microscopes of a given maker. It would naturally be 

 better if it were available for all petrological Microscopes, so that in 

 sending away a preparation for inspection we could easily indicate the 

 point to be observed without an ugly ring of ink. This advantage can 

 be easily attained by the following simple contrivance, which I have 

 adapted to my Microscope for years past and which I have found very 

 effective. 



The stage is divided by lines crossing at right angles, like a chess- 

 board, the distance between the lines being exactly 2 mm. Every 

 fifth line should be somewhat thicker so as to facilitate the counting. 

 It is superfluous to mark the lines with figures. Two of the lines must 

 cross each other exactly in the centre of the stage, and the counting 

 starts from these. When I wish to mark a point in a preparation, I 

 first adjust it in such a manner that the edges of the slide are parallel 

 with the lines. T. then determine the position of one corner (preferably 

 the lower left corner) by coujiting from the two middle lines, and 

 write the result, in the form of a fraction, upon the label of the pre- 



113 

 paration, as for example -=— if the distance along the vertical edge 



78 



(the writing on the preparation being horizontal) is found to be 11 • 3, 



* Amer. Mon. Micr. Journ., v. (1884) pp. 42-3 (1 fig.). 



t Neues Jahrb. f. Mineral. Geol. u. Palaont., 1883, 1. pp. 195-6. 



