364 AIM AKD PROGEESS OF PHYSICAL SCIENCE. 



department of science, can devote but little of our time 

 to the simultaneous study of the other branches. As 

 soon as we enter upon any investigation, all our powers 

 have to be concentrated on a field of narrowed limit. We 

 have not only, like the philologian or historian, to seek 

 out and search through books and gather from them what 

 others have already determined about the subject under 

 inquiry ; that is but a secondary portion of our work. 

 We have to attack the things themselves, and in doing so 

 each offers new and peculiar difficulties of a kind quite 

 different from those the scholar encounters ; while in the 

 majority of instances, most of our time and labour is con- 

 sumed by secondary matters that are but remotely con- 

 nected with the purpose of the investigation. 



At one time, we have to study the errors of our instru- 

 ments, with a view to their diminution, or, where they 

 cannot be removed, to compass their detrimental influ- 

 ence ; while at other times we have to watch for the 

 moment when an organism presents itself under circum- 

 stances most favourable for research. Again, in the course 

 of our investigation we learn for the first time of possible 

 errors which vitiate the result, or perhaps merely raise a 

 suspicion that it may be vitiated, and we find ourselves 

 compelled to begin the work anew, till every shadow of 

 doubt is removed. And it is only when the observer takes 

 such a grip of the subject, so fixes all his thoughts and all 

 his interest upon it that he cannot separate himself from 

 it for weeks, for months, even for years, cannot force 

 himself away from it, in short, till he has mastered every 

 detail, and feels assured of all those results which must 

 come in time, that a perfect and valuable piece of work 

 is done. You are all aware that in every good research, 

 the preparation, the secondary operations, the control of 

 possible errors, and especially in the separation of the 

 results attainable in the time from those that cannot 



