ZOOLOGY AND BOTANY^ MICROSGOPY, ETC. 



423 



Fig. 71, 



Fig. 72. 



Chevalier's Camera Lucida. — Dr. Carpenter describes * a form 

 of this camera intended to be used with the horizontal Microscope. 

 Fig. 71 shows a modification de- 

 signed by Dr. A. Chevalier f for a 

 vertical Microscope. The reflect- 

 ing prism is made much larger 

 and is brought close to the small 

 perforated metal speculum. The 

 whole field is readily seen without 

 any part being obstructed. 



Grunow's Camera Lucida. — 



This camera (ante, p. 120) was 



the subject of discussion at the May meeting of the Society, 

 and for convenience of reference we add fig. 72, showing its con- 

 struction. 



A and B are the lenses of the eye-piece ; D C E, D F E, 

 and G H J three right-angled prisms, the first two having their 

 hypothenuses cemented together with balsam 

 to make a cube. Prior to cementing, the 

 upper of the two prisms has its hypothenuse 

 silvered, but a small spot, not more than 

 l-16th in. in diameter, is afterwards denuded 

 of silver as nearly as may be in the geome- 

 trical centre of the silvered face at M. The 

 prism GHJ is movable on an axis, to pro- 

 vide for its use when the instrument is either 

 upright or inclined. Eays from Z, the table, 

 are totally reflected from the face G H (say at 

 K), and entering the upper prism, are reflected 

 to the eye at X by the silvered surface D E, 

 while the object is seen at the same time 

 through the unsilvered spot in the middle of 

 the same face. 



A writer in the ' English Mechanic ' % says 

 that it is not a sine qua non to silver the 

 surface, but the effect is wonderfully im- 

 proved by doing so, the blue tint that other- 

 wise appears to cover the object being almost 



entirely eliminated by the white reflection from the silver ; and that 

 this form of apparatus can be used with less straining and eye-fatigue 

 than any he ever tried. 



HoUe's Drawing Apparatus.§ — The device of Dr. H. G. Holle 

 differs essentially from all other forms of drawing apparatus, and was 



* ' The Microscope and its Eevelations,' 6th ed., 1881, p. 114 (1 fig.), 

 t 'L'Etudiant micrographe,' 3rd ed., 1882, pp. 167-8 (1 fig.), 

 J Engl. Mech., xxxvii. (1883) p. 1.54 (1 fig.). 



§ Nachr. K. Gesell. Wiss. Gottingen, 1876, pp. 25-7. Cf. Behrens' 'Hilfsbuch 

 z. Ausfuhrung mikr. Untersuch. im bot. Laborat.,' 1883, pp. 90-1. 



