480 Allen and Lahy: Photographic Plates. 



SUMMARY. 



1. Exposure in radiogr.aphy is defined as energy of incident 

 X-rays per square cm. 



2. It is found that within a limited range of exposure the 

 density o^f the developed " imiage " produced in a silver emulsiou 

 is proportioned to the logarithm of the exposure. 



3. The density of the image produced by a given (|uantity of 

 incident energy is independent of the wave length of the radiations- 

 used in these experiments. 



4. The inertia, contrast, and fog density of a number of plates 

 for low radiation intensities is stated. 



5. The speed (that is, the exposure required to produce a givea 

 density) of a plate depends on the nature of the enudsion, and the 

 mass of silver per unit plato area. 



6. Contrast dependsi on the nature of the emulsion and is appa- 

 rently independent of the mass of silver per unit area. 



The experiments are heing continued. 



