PRESIDENT S ADDRESS. 



193 



highest results ; but when this model is confined to small, un- 

 pretentious, well-built instruments, such as VIa, it serves the 

 purpose very well indeed. 



Messrs. Beck and Co. have brought out a penological star 

 microscope,* as well as one of a more advanced type, and 

 Messrs. Swift and Son have improved their Dick microscope.f 



The Zeiss erecting prisms, which are used in the new 

 binoculars, have been applied to a dissecting microscope, J 

 which has also been made binocular after the plan of Cherubin 

 d'Orleans, viz., by using two objectives. 



There is an object-finder § by Herr R. Feuss, which is 

 somewhat similar to that of Bridgman,|| and is for the purpose 

 of scratching a small circle with a diamond point round any 

 desired object. That of Bridgman fits on the objective itself, 

 and must therefore be concentric to it ; but this new device is 

 a separate piece of apparatus, placed on the nose-piece when 

 the objective is removed, and not necessarily concentric. 



In the optical department we have an apochromatic 1-| inch 

 objective by Powell, and a semi-apochromatic of the same 

 power by Zeiss, their optical indices being 27 and 31 

 respectively. 



Mr. J. W. Gifford has produced a beautiful F line screen, 

 which far surpasses all previous attempts in this direction. It 

 passes plenty of light, and while it does not interfere with 

 vision, so far as the eye is concerned, it nevertheless sharpens 

 up even apochromatic objectives, and brings the cheap semi- 

 apochromats almost to the same degree of efficiency as apochro- 

 mats. Finally, it slightly increases the resolving power by 

 shortening the wave length, that is by filtering out the visually 

 more luminous longer waves. I cannot too strongly urge mem- 

 bers to supply themselves with so cheap and efficient piece of 

 apparatus. 



Two articles have appeared in the " Journal R.M.S." on 

 " Brownian Movement."^ Will not some member take up and 



* Tom. cit., p. 226, 3 figs. 



f Id., p. 96, fig. 6. 



t Id., p. 5S0, 3 figs. 



§ " Journ. R.M.S.," 1895, p. 587, 2 figs. 



|| " Quart. Journ. Mic. Sci.," 1855, Vol. iii., p. 237. 



IF "Journ. E.M.S./' 1895, pp. Ill, 591. 



Journ. Q. M. C, Series II., No. 38. 14 



