472 ]Visco7isin Academy of Sciences, Arls, and Letters. 



Then if ^ve put the side 6 = 90° in order to simplify the com- 

 putation and to obtain a representative value from vv^hich the 

 others differ but little, the formula / (c) is changed as follows:. 



fU-) - ^- s-:n 2^ I -^"^^ ^^ (/'x+/'.-f/\ )+/'5-/'7+/"3 \ 



Then, after Tve have written for the various quantities f and 

 /", their values according to § 12 there are seen to be 27 sources 

 of error, and 



1/ 2»i 



whence it follows that 



wF[c) = 10-6 -^ /:2{a') 



The values oi w F (c) corresponding to different values of A 

 will be; 



A wFic) 



