for the Measurement of Visibility of Objects. 107 

 solving equation (1), for B t , we obtain, 



B B =fc^? (4) 



Now, B 2 = E 2 .R 2 (5j 



... B P = B '~^ R ' (6) 



Also ' V s =^ (7) 



Therefore, v _ Bi — cE 2 U 2 



V h = 



As previously shown, 



4 - B x (<-1) 



=^i-(|- R2 ^t)- • • (8 > 



therefore 



v 6 



w =l'- • p> 



Vs = c 4i-(w E2 -^i)' 



= (w- E -i^)-ii- • • -( 10 > 



Equation (10) is a general expression of brightness visi- 

 bility as a function of both W and R 2 . 



Now, in evaluating the constant c it is found that there 



are two possible values, one in case — > Jc, and one for the 



-Do 

 1 B l 7 



case where =~- < k. 

 Case L, — - >k, c = k, 



&2 



v ^(w- R -ii)-ii- • • • (ID 



Case II., -p. 1 <k, c= - 



Jt> 2 & 



v -(w-Ai=i)--i=i • • • ( 12 > 



Equations (11) and (12) now express visibility as a function 



