at the total solar Eclipse in 1882 351 



the line B.,,B 4 . But 4 B 4 is the direction of the incident ray 

 at B ; therefore B 4 A is the direction of the reflected ray, and 

 the ray which strikes the outer rim of the mirror is reflected 

 upon the upper extremity of the focal line. In the same way 

 it is evident that the incident ray O 3 B 3 , which strikes the 

 inner rim of the mirror, is reflected along the line B 3 B and 

 falls upon B, the lower extremity of the focal line. Conse- 

 quently parallel rays which strike the mirror in points between 

 B 4 and BS are reflected on AB and strike it in points between 

 A and B which are homologous as regards position with the 

 points in the mirror between B 4 and B 3 which are struck by 

 the primary rays. 



In the isosceles triangle B 3 A S B 4 the angle A 3 is equal to 

 the angle A 3 AB, therefore 



A AB 



therefore A 3 = 1 1 1 48' ; 



and the angle at the base 



Further, the base 



B 3 B 4 = 2 x AB cos / = 3-3 1 inches. 



Therefore the width (; 3 ) of the outer mirror is 3-3 1 inches, 

 and it is inclined to the axis at an angle of 34 6'. 



The radius of the upper rim of the outer mirror is 

 AB 3 + DsB 4 = AB 3 + B 3 B 4 sin 2 = 5 + 3-31 sin 34 6' = 6-85 inches. 



Further, if the line B 4 B 3 be continued till it cuts the axis 

 in B s ', then B 4 B 3 is the generating line of the complete cone 

 of which the outer mirror is a portion. 



Its length is obviously 



-?, = I2'23 inches. 

 sin 34 6 



The width of the mirror is 3-31 inches. Therefore the 

 annular band of silvered metal has an outer radius of 12*23 



