35 2 On a solar Calorimeter used in Egypt 



inches and an inner radius of 8*92 inches, and the sector to 

 be removed from it has an amplitude of 



12-23-6-85 



360 - = K8 J 's. 



12-23 



Inner Mirror. Through B z draw O 2 P 2 , and on it lay off, 

 below the line BB^ the length R 2 A 1 = BA = 2 inches. From 

 A! at distance A^B* describe a circular arc. Join A 1 B. This 

 line cuts the arc in B^. Join Z?,/? a . L\B., is evidently the 

 line of section of the inner mirror. The demonstration is 

 the same as in the case of the outer mirror. 



Also 



Az> 



' A = 56 19', 



whence *j = 6i5i', 



and /! = 2 . A B cos t\ = i -88 inches. 



Therefore the inner mirror has a width of r88 inches and is 

 inclined to the axis at an angle of 61 51'. 



Further, if B^B^ be continued to cut the axis in B{, B^Bf 

 is the length of the generating line of the complete cone of 

 which the mirror forms a part, and it is the greater radius 

 of the annular disc of silvered metal out of which the band 

 is to be cut. Its length is 



BB Z 



, " --, = 3-40 inches. 

 sm6i 51 



The inner radius of the annular disc is 1-52 inches, and the 

 amplitude of the sector to be removed is 



jso-e-j.^'-j. 



The numerical data just worked out and relating to the 

 reflector used are collected in the following table. 



The condition that one of the mirrors should be inclined 

 at an angle of 45 to the axis was suggested by the fact that 

 this is the angle of greatest efficiency and by the consideration 

 that it is an angle which is familiar in mechanical workshops, 



