810 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Sliding-objective Changers and Revolvers.* — Among devices for 

 saving time when an operator has to work with more than one objective, 

 revolving nose-pieces are the best and most successful. P. K. Studnicka 

 points out, however, that objectives used in this way are liable to errors 

 of centring, and that in high-class work such errors may become im- 

 portant. Another, and perhaps more serious difficulty, is the limitation 

 to the possible number of objectives on a revolver. More than four 

 cannot be applied, and they are apt to interfere with the manipulation of 

 the ]irep;u - ation-slide. The number on one revolver seldom, therefore, 

 extends beyond three. With an objective-slide some of the above dis- 

 advantages disappear ; there is no restriction as to number, and everyone 

 can adjust the centring without tedium. On the other hand, exchange 

 of objectives is a longer operation than with a revolver. The author 

 expresses his surprise that no attempt has yet been made to combine the 

 ml vantages of both systems; and that the revolvers themselves might 

 be interchangeable, and be attached to the Microscope-tube by some 

 sliding movement. In this way an operator might work with, say, two 

 revolvers : one with his weak, and the other with his strong objectives. 



Methods for the Identification of Sub-microscopic Structures.! — 

 J. Koenigsberger has made use of Lippmann's layers in colour photo- 



Fig. 91. 



c = 2") u 



022 a 



graphy for obtaining a natural grating. If the film obtained by blue- 

 violet light be sectionized obliquely by a microtome (fig. 91) and mounted 

 in damara in the usual way, then a grating is obtained in which the 

 layers of silver granules are separated by intervals varying from one- 

 third to four times the wave-length of yellow-red light (A = • 6 /a), see 

 fig. 92. Resolution through the end at which the layers are distant from 

 each other less than a wave-length is of course impossible, but the polari- 

 zation effects obtained give a clue to the structure. The author describes 

 fully the nature of the auxiliary polarizing apparatus required. 



New Zeiss Nernst Lamp. —This lamp (fig. 93) consists of a single 

 filament in globular metal casing, nickel plated, and so arranged that the 

 upper half readily removes, leaving free access to the filament which is to 

 be started with a spirit flame or wax match after the current is switched 

 on to render it incandescent. A small chimney to draw off the heat of 



* Zeitsch. wiss. Mikrosk., xxvii. (1911) pp. 501-3. 



t Zeitschr. wiss. Mikr., xxviii. (1911) pp. 34-41 (2 figs.). 



X Pamphlet on Ultra Microscopy, pt. 4, figs. 1 and 4. 



