648 SUMMARY OF CURRENT RESEARCHES RELATING TO 



action on thinly deposited silver. The author, however, used the ordi- 

 nary " hypo " bath. 



Excellent paper negatives were obtained with rapid bromide papers, 

 and also with gas-light papers. On printing positives from them in 

 the ordinary way, the grain of the paper negative disappears, as it is auto-, 

 matically compensated by the grain within the paper which gave rise to 

 it. Printing-out papers also give negatives which can be used for print- 

 ing positives on bromide paper without previous toning and fixing, but 

 the exposure has to be very long. 



In applying the process to black or white originals, certain advantages 

 are gained over the ordinary methods with the camera : — 1. The repro- 

 duction is of the exact size of the original. 2. The sharpness of defini- 

 tion is only limited by the size of the silver grain in the plate. 3. All 

 differences in the angle of reflection of light by the original are avoided, 

 all the effective light emerging at right angles to the surface. 



Chronophotomicrography.* — L. Chevroton points out the importance 

 of photographing moving objects at known intervals of time, and 

 describes the arrangements she has successfully used for the purpose. 

 She employs a Zeiss optical bench with the usual fittings and a voltaic 

 arc, as light source, of 20-25 amperes and 60 volts continuous current. 

 But in front of the water cooler a sector-disk is inserted capable of 

 revolution at a known rate. Thus, if a sector cuts the optical axis 

 30 times a minute, and the interval between the sectors is about 11°, 

 30 images are received per second and each of these has ^^ in. of 

 pose. A Zeiss stand is fixed vertically on the general support of the 

 camera and independently of the optical bench ; the chronophotographic 

 apparatus is itself in a direct connection with the stand by means of a 

 telescopic tube in order to avoid all loss of light, an essential condition. 

 The sector-disk may be operated by hand or by a motor. 



Mirror-reflex Camera for Photomicrography.! — This apparatus 

 was designed by W. Scheffer mainly for instantaneous photomicro- 

 graphy, but has been found to succeed well with either transparent 

 light or with dark-ground illumination. It has, therefore, been found 

 useful to the microscopist for other purposes, including that of the 

 cinematography of microscopic objects. The task before the designer 

 was to devise an arrangement by which the movements of the object 

 could be observed on the ground-glass screen, while at the same time 

 all the arrangements necessary for photomicrography were in readiness 

 and could be brought into instantaneous action. Fig. 112 shows dia- 

 grammaticaUy the principle of the apparatus. Two mirrors, A and B, 

 are arranged in a wooden case. The beam of rays proceeding from the 

 Microscope comes through 0, and is. twice reflected at the mirrors A 

 and B on to the ground-glass screen M. The ocular end of the Micro- 

 scope is connected in light-tight fashion by the customary funnel with 

 O. In V is a window arrangement, which is opened when the mirror A 

 is rotated round the axis I) from the position D E into the position 

 D E'. If the window V is opened, the light of the Microscope travels 



* C.R. Soc. de Biol., lxvi. (1909) pp. 340-2 (1 fig.). 



t Zeitschr. wiss. Mikrosk., xxvi. (1909) pp. 111-15 (3 figs.). 



