[ 39 + ] 
at all 19 known antecedently to any trials made or ob- 
served concerning it. And fuch an event I fhall call 
an unknown event. 
Cor. Hence, by fuppofing the ordinates in the fi- 
gure A i B to be contracted in the ratio of E to one, 
which makes no alteration in the proportion of the 
parts of the figure intercepted between them, and 
applying what is faid of the event M to an unknown 
event, we have the following proportion, which gives 
the rules for finding the probability of an event from 
the number of times it actually happens and fails. 
PROP. io. 
If a figure be deferibed upon any bafe A H (Vid. 
Fig.) having for it’s equation y — x p r ? -, where y, 
x , r are refpedtively the ratios of an ordinate of the 
figure inlifting on the bafe at right angles, of the 
fegment of the bafe intercepted between the ordinate 
and A the beginning of the bafe, and of the other 
fegment of the bafe lying between the ordinate and 
the point H, to the bafe as their common confequent. 
I fay then that if an unknown event has happened 
p times and failed q in p -|- q trials, and in the bafe 
AH taking any two points as f and t you eredl the 
ordinates f c, t F at right angles with it, the chance 
that the probability of the event lies fomewhere be- 
tween the ratio of A f to AH and that of A t to 
AH, is the ratio of t¥ C f that part of the before- 
deferibed figure which is intercepted between the two 
ordinates, to ACFH the whole figure infilling on 
the bafe A H. 
This is evident from prop. 9. and the remarks made 
in the foregoing fcholium and corollary. 
c Now 
