C 543- ] 
film to unity , the like complement of the product oj 
the four fines of the fdes and, angles ; and the fquare 
root oj the quotient fhall he the fine of half the unknown 
angle.. 
If we work by logarithms, the operation will not 
be very troublefome ; but the rule needs not be ufed, 
unlefs when a table of the trigonometrical analogies 
is wanting. To fupply which, the foregoing theo- 
rems will be found Sufficient, and of "ready ufe - 
being either committed to memory, or noted down 
on the blank leaf of the trigonometrical tables. 
Note, The fchemes may be better, raifed in card- 
paper, or with bent wires and threads. 
LXXL An Account of Two extraordinary 
Cafes of Gall-Stones . By James John- 
ftone, M. D. of Kidderminfter. Com- 
municated by the Rev . Charles Lyttelton, 
jL. JL. D. Dean of Exeter. 
To the Rev. Dr. Lyttelton, Dean of Exeter. 
Rev. Sir,. 
Read Feb. 9, Ccording to promife I fend you a 
ffiort account of the two extraor- 
dinary cafes we talked of, the laft time I had the 
pleafure of feeing you at Kidderminfter. 
The truth of the iirft narrated cafe you are already 
a fufficient judge of j. and if it is at all neteftary to 
afcertain 
