WILLIAM R. AMBERSON 527 



distribution of the Cypridina luminescence. I have sought to achieve 

 the desired results in another way. 



The method finally adopted makes use of the Cypridina light 

 itself for the impressing of calibration exposures. Two-thirds of 

 the width of the film strip is given over to the moving records. Upon 

 the other third there is impressed a series of fifteen calibration 

 exposures, Plate 1 illustrates several typical records which indicate 

 the results of this method. 



The fifteen caHbration exposures are impressed simultaneously 

 through a series of fifteen windows in which are placed neutral photo- 

 graphic filters of various known transmission values. Measurement 

 by the pyrometer has indicated that the filters used are very nearly 

 neutral throughout the blue and green regions of the spectrum; that 

 is, throughout that region in which Cypridina light affects the film. 

 Absolute neutrality in such screens is impossible of attainment. 



The series of filters are mounted in windows cut in a brass strip, 

 wide enough to shield the whole width of the film, and bent in the 

 form of the arc of a circle with a radius of 15 mm. (Fig. 2). At the 

 center of this circle a test-tube 25 cm. in diameter is mounted. The 

 test-tube is painted a flat black with the exception of a segment, A , 

 which gives a ring of light at the level of the windows, when reacting 

 Cypridina solutions are placed in it. After the moving records of 

 the luminescence have been impressed upon the lower two-thirds of 

 the film, the latter is clamped tightly between the brass strip, B, 

 carrying the filters, and a rigid back, C, bent to the same curvature. 

 Fifteen spots on the unexposed third of the film are thus brought 

 opposite to the fifteen openings in strip B, all spots being equidistant 

 from the ring opening in the test-tube at the center. A concentrated 

 luciferin solution is placed in the test-tube, a motor driven propeller 

 sets the whole solution into rapid rotation, and a concentrated enzyme 

 solution is added. The resulting illumination of the ring opening A 

 presents an absolutely identical light source to all of the fifteen 

 windows simultaneously. This illumination is indeed not constant, 

 but falls rapidly through the typical curve of decay characteristic 

 of the reaction. This rapidly diminishing light source, however, 

 exerts an identical effect in every direction at each instant, and the 

 only differential factor in the light which reaches the fifteen spots 



