678 SUMMARY OF CURRENT RESEARCHES RELATING TO 



by P. Waechter, of Berlin, is specially adapted for travelling, as when 

 closed, it forms a box of only 10 cm. in length by 10 cm. in breadth 

 and 7 cm. in height. The two halves of the cover a, opening right 

 and left, serve as supports for the hand. Inside the box is the stand 

 b with the stage and mirror, as well as the receptacles c for keeping 

 the three achromatic objectives of 15, 25, and 40 power. The re- 

 maining space can be utilized for other apparatus. 



Measurement of the Power of Eye-pieces.* — Dr. Eoyston- 

 Pigott originally suggested the placing of the eye-piece in the sub- 

 stage and throwing an image of a rule, supported at a distance of 10 

 inches from the diaphragm of the eye-piece, upon a stage micrometer. 

 Mr. W. H. Bulloch having found considerable difficulty in getting the 

 lines of the rule sharply defined, has devised an apparatus consisting 

 of an ordinary Microscope with an objective of 2 inches focus, used 

 to examine an image of a diaphragm, formed by the eye-piece to be 

 measured. The exact size of the diaphragm and its distance from the 

 eye-piece being known, the size of the miniature image formed by 

 the eye-piece can be readily measured, and a simple calculation then 

 gives the magnifying power. 



Hall's Eye-protector for use with the Monocular Microscope.t 

 — Dr. L. B. Hall describes an appliance to be used with the mono- 

 cular instrument, for the purpose of protecting the unemployed eye, 

 pointing out that the employment of one and the same eye at the tube 

 of an optical instrument is the same practice that cost the squinting 

 eye of childhood its power of vision. So many of us are contented at 

 having trained one eye to do acceptable work, that we think we cannot 

 spare the time to discipline the other. If this process ended when 

 the head is withdrawn from the instrument, the practice would be less 

 dangerous, but the trained eye finding an unequal companion, performs 

 reading and all other near work with greater ease than its fellow ; 

 sees so much more distinctly that the other is left without exercise, 

 except for large objects, and becomes of less and less value as tho 

 process goes on. Dr. Hall could point, he says, to those who have 

 practically lost one eye by this process, and estimates that one-half 

 of all those who have used the monocular Microscope to any con- 

 siderable extent during five years are monocular men for all fine 

 work, meaning by this that every such person who can " resolve " one 

 of the more difficult tests with one eye will find himself unable to do 

 so with the other. 



How often have we heard persons exclaim, upon looking into a 

 binocular Microscope for the first time, how much easier it is to see 

 with the instrument, and this with one field quite dark ; such ex- 

 pressions are not to be ascribed wholly to dissimulation, or flattery, 

 and for the following reasons, viz. : — When both eyes are left open 

 and one is applied to an instrument, the two images, being unlike, 



* Amer. Mon. Micr. Journ., iii. (1882) pp. 103-4 (1 fig.)- ' The Microscope,' 

 ii. (1882) pp. 83-4. 



f ' The Microscope,' ii. (1882) pp. 88-90 (from the ' Medical and Surgical 

 Reporter '), 



