90 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



calculation have been tried in the past and abandoned, but the failure of 

 any one system need not mean the failure of all systems resting on a 

 similar basis. The question of success or failure appears to be largely 

 determined by what may at first sight seem to be quite minor details in 

 the application of approximate methods. It will be necessary to justify 

 the new methods suggested for use by including a large number of 

 fully worked examples illustrating applications to a considerable variety 

 ■of optical problems. • 



Microscopes. — A number of requests have been made from time to 

 time for certificates for microscope objectives, eye-pieces, and other 

 apparatus. It is evident that the institution of regular tests of this 

 kind, as distinct from the unsystematized tests hitherto made, would meet 

 a generally felt want. As in the examination of many other optical 

 instruments, such as high-class photographic lenses, the tests will only 

 •carry the necessary authority if they are made by admittedly expert 

 workers. 



Before the tests can be standardized it will be necessary to acquire 

 typical specimens of the various objectives produced by different manu- 

 facturers at home and abroad. In some cases the qualities of objectives 



are largely a function of the price at which they 

 are sold, and it is not altogether justifiable to 

 demand the same standard from expensive and 

 cheap objectives having approximately the same 

 fundamental properties. Additions are also re- 

 quired to the microscope equipment of the depart- 

 ment for general laboratory work. 



Standard London Microscope (manufactured 

 by R. & J. Beck, Ltd., 1020).— The base of this 

 microscope is on the so-called horse-shoe pattern, 

 standing on three feet. 



The pillar has a joint for inclination. 

 The stage is completely covered with ebonite 

 and is 4 in. wide. The free distance from the 

 optical centre to the limb is 3 in. 



The mechanical stage is attached to the 

 microscope by means of a bolt which passes 

 through a hole provided for the purpose in the 

 limb of the instrument. It has slightly over 1 in. 

 vertical and 2 in. horizontal travel, each provided 

 with divided scales. 



The draw tube is nickel-plated, and is divided 

 in millimetres, enabling any tube length l)etween 

 140 and 200 mm. to be used. 

 The coarse adjustment is by means of spiral rack and pinion, cut on 

 specially made machines to secure accurate and smooth running teeth. 



The fine adjustment is on a new patented design in which both 

 milled heads are upon the same axis, but the whole of the complicated 

 cams and worm wheels generally adopted for side slow motions are 

 dispensed with, and the movement is imparted by the point contact of a 



