324 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



micrography. It supports the source of illumination a, the con- 

 densers, and the condensing lenses; (2) the microscope c placed on 

 a socket resting on a platform free of vibrations; (3) a heavy metal 

 structure that supports the moving picture apparatus /; and (4) 

 a lateral steel table on which are fixed the movable parts and the 

 shutter d which periodically cuts off the light ray between the lamp 

 and the microscope. An electric motor e placed under this table 

 on the floor activates the different movements. 



These four parts and the electric motor have their bases sealed 

 into a concrete block sunk into the floor. The vibrations produced 

 by the functioning of the apparatus as well as the vibrations of the 

 street and building are easily reduced by this large mass; no vibra- 

 tions whatever are transmitted to the optical part of the apparatus. 



The large Zeiss photographic microscope c with its different optical 

 combinations of objectives and oculars is generally used for the work. 



The sources of illumination differ according to the photographs 

 taken; they are: An arc lamp with continuous current of 20 amperes, 

 or an incandescent lamp (automobile head light of 100 candlepower, 

 12 volts), or the Koehlcr apparatus — a spark between cadmium 

 electrodes, the prism and optics of quartz for maldng moving pictures 

 in ultraviolet light. 



The upper part of the table, supporting the lamp and the optical 

 bench, is placed on a slide screwed into tliis heavy structure. It can 

 thus be shifted horizontally, parallel to the optical bench, especially 

 when it is desirable to photograph preparations in a vertical position; 

 the microscope tube is thus inclined about 90° horizontally to the 

 axis of the light ray projected by the lamp. A prism with total 

 reflection, fixed to the ocular, reflects the light ray forming the image 

 upward vertically to the center of the \\'indow framing the film. 



Generally, the photographs were taken by means of the vertical 

 microscope as the photographs show in plates 1 and 2. The light 

 ray falls on the center of the mirror of the microscope, then is reflected 

 perpendicularly according to the optical axis of the microscope, and 

 terminates as in the preceding at the \\indow of the apparatus. 



The apparatus for taking the mo\'ing pictures/ is a G. V. Debric, 

 modified according to the directions of Dr. Comandon. This remark- 

 able apparatus of great speed (which was created by Labrely) permits 

 taking more than 250 ^aews per second. At this speed, the system of 

 catches which pulls the film causes the substitution of one image after 

 another in less than one five-hundredth of a second. Such great 

 speeds are used in moving photomicrographs only for analyzing very 

 rapid movements; at lower speeds, this apparatus has the great ad- 

 vantage of increasing the length of time of pose for the usual speeds 

 of motion pictures. 



