vSv30 KINETICS OF BIOLUMINESCENT REACTION. I 



direct transmission through the spaces between grains. In addition 

 there is a considerable amount of Hght which is first incident upon the 

 grains themselves, and is then thrown through the screen at various 

 angles by reflection from them. Such additional light forms the 

 "scatter" or diffusion component. The amount of light actually 

 transmitted and available for affecting the film is the sum of these 

 two components thus directly and indirectly transmitted. In the 

 evaluation of such filter transmissions both compounds are auto- 

 matically taken care of by measuring the percentage of reduction by 

 the filters of the light from a completely diffusing background. For 

 this purpose I have used an opal glass screen illuminated by a 200 

 watt Mazda lamp run at constant voltage. The filters to be measured 

 are set in immediate contact with this diffusing screen, so that the 

 diffusing surface is in exactly the same position with reference to the 

 filter as is the film at the time of the calibration exposures. The 

 transmission values are then read off with the pyrometer, with which 

 a blue screen is used. It seemed advisable to check the transmission 

 values so determined by some other method in order to be absolutely 

 sure that these values correctly represented the photographic effect. 

 By a photographic method a parallel set of values were obtained 

 which checked the pyrometer determinations within the error of the 

 photographic material. The pyrometer values have been accepted 

 as being probably the more accurate. 



The calibration method just described has proven a rapid and 

 satisfactory way of impressing calibration exposures which upon 

 development give a series of densities whose corresponding previously 

 incident relative intensities are accurately known. From these 

 values a curve of blackening similar to Fig. 1 is drawn for each experi- 

 ment, and densities read along the moving records are referred to the 

 standard curve for evaluation. Extrapolations for short distances 

 in both directions beyond the experimental points are usually used, 

 permitting a range of reading in good records of as much as 100 per 

 cent to 0.5 per cent in light intensity. The average range is about 

 half of this. 



In developing films, the records, emulsion side out, are fastened 

 upon a strip of glass of the same length. The whole film is immersed 



