392 APPENDIX CALCULATION OF THE 



2. To find \ their difference. 



tang. |(/ 6 -/ 7 ) = t.^32'30"sin.4'15'33' 



sin. 28 10' 25" 



log. cot. 52 32' SO" z= 9-8843264 

 log. sin. 4 15' 32" 8-8707728 



18-7550992 

 log. sin. 28' 10' 26" z= 9 6740791 



log. tang, i (/ 6 / 7 ) = 9 0810201 



Therefore f (7 6 / 7 ) = 52' 18" 

 Therefore 



/ 6 = 40 55' 2" -f 6 52' 18" 47 47' 20" 

 I 7 = 40 55' 2" 6 52' 18" = 34 2' 44" 

 and the inclination of the plane efg is con- 

 sequently 



on P = 180 47 47' 20" = 132 12' 40" 

 F 18034 2' 44" 145 57' 16" 

 which are very nearly the angles we are sup- 

 posed to have found by measurement of the 

 crystal, as given in p. 384, and from which we 

 deduced the l^w of decrement we have here 

 supposed to be known. 



The instances here selected to illustrate the me- 

 thods of calculation previously described, are among 

 the most complicated that are likely to occur: and 

 they have been so selected, because they contain more 

 of the varieties of formulaB than will commonly pre- 

 sent themselves during our researches. 



