SELIG HECHT 



239 



k being a constant. The deviations of the average experimental 

 points from the theoretical hyperbola of Fig. 5 are not great. In fact 

 the probable error of any individual determination is 6.7 per cent of 

 the mean value assimied in drawing the hyperbola in Fig. 5. 



0.02 0.04- a OS 0.08 



OJO 



Fig. 5. Relation between exposure and minimum intensity necessary for a 

 response. The points are the average experimental values. The curve is an 

 hyperbola, /•/ = 5.62, drawn from the theoretical expectation of the Bunsen- 

 Roscoe law. 



