60 MODES OF RESEARCH IN GENETICS 



Whatever the material of scientific investiga- 

 tion, whether animate or inanimate, it is a 

 fact of universal experience that just as soon 

 as observation or experiment concerns itself with 

 any quantitative aspect of a phenomenon it 

 is impossible ever to get precisely the same 

 result twice. The more refined and delicate the 

 instrument, and the finer the units in which the 

 measurement is made, the more evident does it 

 become that the "absolute" determination of 

 any magnitude whatsoever is humanly impossible. 

 The problem of all quantitative science, therefore, 

 is to determine with a maximum of accuracy the 

 probability that any particular unknowable magni- 

 tude lies within any assigned limits. One never 

 can say, and be scientifically accurate, that a 

 particular stick is precisely 11.5 cm. long, but if 

 it be worth one's while, it is possible to determine 

 the mathematical probability that the true length 

 of the stick lies between say 11.498 and 11.502 

 cm. In the writer's opinion it must be regarded 

 as the point of greatest value of statistical theory 

 for science in general that it furnishes the method 

 of determining such probabilities. 



That the probable error concept is of high im- 

 portance for biology is so evident as not to need 

 lengthy discussion. When one considers what a 

 large part of the results of experimental investi- 

 gations of all kinds of physiological topics (to 

 take but one instance) are quantitative in charac- 



