16 PLANT PHYSIOLOGY 



the obvious ones arising from carelessness, clumsiness, or othei 

 personal incapacity, for the student of such characteristics will 

 stop short of this course. But of the legitimate personal errors 

 there are several, against which the student should be forever 

 and consciously on guard. Thus, in matters involving obser- 

 vational judgment, as when spaces of time or distance must 

 be read by estimation, the personal equation, a well-known 

 source of error, intrudes. It can be met only by ascertaining 

 one's own tendency, whether too fast or too slow, and by constant 

 comparison with the averages obtained from many others. A 

 common and concrete personal error lies in a tendency to mis- 

 read fractional parts, as of degrees, weights, etc., when hurried, 

 the more especially if the scale must be read inverted. The 

 remedy is this, never to be hurried, and also to cultivate the 

 habit of always reading such figures twice, if possible in a 

 reverse direction or in a different frame of observational mind. 

 And especially the habit should be formed of concentrating 

 the whole attention upon that one single thing for the moment, 

 with a conscious effort and resolve to read correctly. When 

 the results of any given study are mathematical, there are mathe- 

 matical methods, more or less easy of application, for determin- 

 ing the probable error. There is, however, a simpler way which, 

 for most student work, is practically effective, namely, to com- 

 pare one's own results with the mean of those obtained by other 

 students working at the same time upon the same problem. 

 To establish such a mean it is needful that all should work by 

 the same methods and express their results in the same units. 



5. Errors 0} the Mind. These arise from the fact that the 

 mind, our only tool for the investigation of the abstract and 

 the unknown, is an excessively poor one for the purpose, because 

 it was developed in adaptation to efficiency in a totally different 

 direction, namely, material success in a struggle with a world 

 of concrete fact. Hence we have a sense of impotence in the 

 presence of the unknown which makes us willing to rest content 

 with mysterious, metaphysical, or even complexly verbal ex- 

 planations, without demanding clear definition and evidence 



