172 Benjamin Peirce. 
graphic method. ‘The whole subject of errors of observations, 
the law of facility of error which is assumed in the method of 
east squares, its limits and defects, and the habits of observers, 
were carefully examined. The method of occultations was de- 
cided to admit of greater accuracy than any other that was then 
available, and the occultations of the Pleiades to furnish the 
most convenient means of its application. Formule and tables 
_ were prepared, old observations collected, and new ones made 
oughly treated, will always be of practical import. 
t seems as though there was a connection between this en- 
gagement with the Coast Survey and the appearance, in July, 
1852, in Gould’s “‘ Astronomical Journal,” of an article by Pro- 
fessor Peirce, entitled, “Criterion for the Rejection of Doubtful 
Observations.” His object was to solve this problem: There 
being given certain observations, of which the greater part is to 
be regarded as normal, and subject to the ordinary law of error 
adopted in the method of least squares, while a smaller un- 
known portion is abnormal, and subject to some obscure source 
of error, to ascertain the most probable hypothesis as to the 
partition of the observations into normal and abnormal. This 
method or rule given for deciding whether an observation had 
better be left out of account has received the name, “ Peirce’s 
e 
tions to science. ‘'ables for use in applying it were soon after- 
ward published by Dr. Gould. 
Th 
that discordance. at the mind thus instinctively «ces, there 
must be basis at least for a rule for doing. Professor Airy s 
objections were answered by Professor Winlock at the time of 
their appearance. The “Criterion” has been used considerably 
in this country, though not, perhaps, in Europe. The uniform 
testimony of our computers is, we believe, that it has given €X- 
cellent discrimination, and that it does not come into conflict 
with proper judgment based upon experience. This shows the — 
good working of it in actual practice. 
That the “Criterion” has not come into use in Kurope may 
