278 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



together, as in a pair of compasses. It then packs into a box 20 cm. 

 by 10 cm. and 5 cm. deep. 



The instrument was designed by M. C. Verick, with the co-opera- 

 tion of Dr. L. Malassez. 



Abbe's Camera Lucida.— We have already recorded the two or 

 three paragraphs which have appeared as to this instrument,* and now 

 add a figure of it taken from the 2nd edition of Dr. Dippel's work f 

 (fig. 48). 



The glass cube (consisting of two prisms, with an hypothenuse 

 surface partly silvered, and leaving a small hole in the centre) is at 

 W, the reflecting mirror at Sp, the eye at O. The rays from the 



Fig. 48 



paper come in the direction S2, and are reflected first by the mirror, 

 and a second time by the silvered prism to 0, while the object is seen 

 through the small hole in the silvered surface. 



Herr E. Giltay % writes of it with approval, both for low powers 

 and also for high powers when tinted glasses are interposed to 

 reduce the brightness of the drawing-surface, as described by Dr. 

 Dippel, ante, p. 119, an improvement which Herr Giltay claims the 

 credit of suggesting. 



The rest of the article is devoted to what is described in the 

 heading " as an improvement applicable to cameras in general," which 

 is simply the very old expedient of introducing suitable lenses between 

 the eye and the paper, but which the author writes of as if it were 

 a new and important discovery now made by him for the first time ! 

 The following observations on the theoretical reasons for the benefit 

 obtained by the lenses may be quoted. 



Those who are accustomed to use the Microscope allow the accom- 

 modation of the eye to remain nearly quiescent. Just for this reason 

 one can bear for so long a time without fatigue work apparently so 

 trying to the eyes. With the camera, however, one is naturally obliged 

 to accommodate the eye to the drawing-surface. In ordinary binocular 

 vision drawing does not present so many difficulties to normal eyes, 

 because, first, the paper is held at a convenient distance before the 

 eyes, and, secondly, the required accommodation is guided and assisted 



* See this Journal, ii. (1882) pp. 261, 593, ante p. 119. 

 t 'Das Mikroskop,' 2ad ed., 1882, pp. 631-2 (1 fig.). 

 X Bot. Centralbl., xiii. (1883) pp. 419-22. 



