108 Mr. Loyd A. Jones on a Method and Instrument 



of the variables R 2 and W for the two cases covering all 

 values of the ratio 



h 



If in these equations R 2 he treated as a constant they then 

 express visibility in the form V 6 =/(W) ; while if *W be 

 -treated as a constant they express' visibility in the form 

 V 6 =/(R 2 ). 



Now the value of the contrast constant k can be deter- 

 mined from the sensibility carve, fig. 2, for any specified 

 value of Bj. Let a value of k = V02 be assumed and then 

 by assuming a series of values for R 2 a family of curves 

 showing V as a function of W can be plotted. These curves 

 are given in fig. 3, the ordinate values being visibility, V B , 



Kff. 3. 



VISI6IL1TY (V) 



8 5 o o r o 



Visibility as a Function of the Weather Coefficient. 



and the abscissae values the weather coefficient, W. It will 

 be seen from fiV. 3 that 



Case I., ~ > k, 



is represented by a group of rectangular hyperbolas having 



