ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 



483 



The face-holder has a chin-rest capable of being raised or lowered, 

 and is marked on either side with two white lines indicating the position 

 the patient's outer cauthi should occupy. 



The instrument is made in two forms, one mounted on a table stand, 

 as illustrated, and the other with a tripod floor-standard on castors. 

 The upright of the stand contains a helical spring which counter- 

 balances the superincumbent weight and facilitates the adjustment of 

 the instrument to the height of the patient's canthi. The whole of the 

 upper part of the instrument can be removed and the ophthalmic 

 Microscope or any other apparatus substituted. 



The ophthalmic Microscope (fig. 78) consists of a body with draw- 

 tube and R.M.S. gauge for objective and eye-piece. 



i 



Fig. 78. 



The electric illumination is inclosed in a cylinder and mounted on 

 the body in such a manner as to admit of free orientation. It is pro- 

 vided with a condenser, adjustable to give either a parallel beam or a 

 converging pencil, and has also a carrier for tinted glasses. 



Objectives ranging from 3 in. to 1 in. can be employed. 



DiECK, W. — Das Photomikroskop fiir ultra violetten Strahlen und Seine Bedeutung 

 fur die Mstologische Untersuchung. 



SB. Ges. Naturf.-Freunde, Nos. 1-5, Berlin, 1905. 



(2) Eye-pieces and Objectives. 



Measurement of Highly Curved Lenses with the Abbe Sphero- 

 meter.* — H. C. Lomlj shows that the formula usually applied, viz. : 



is not sufficiently accurate for highly curved lenses. (Here R = requh'ed 

 radius of curvature ; h the lens thickness as measured by the instrument ; 



* Deutsch. Mech.-Zeit., 1907, pp. 15-17 (2 figs.). 



