64 POPULAR SCIENCE MONTHLY. 



about one per cent., and it is said that experts can distinguish the 

 difference of a fraction of a degree centigrade by the temperature sense 

 alone. Now while the other senses may distinguish two or more kinds 

 of extension, as, for instance, pitch and loudness in the case of hearing, 

 vision is the only sense with quantitative perception in which the ex- 

 tensions are identical in every respect except in their relation to direc- 

 tions, thus giving a field of vision so-called within which individually 

 different marks may be compared. The eye is capable of judging the 

 coincidence of two abutting lines to one minute of arc, which is a 

 more sensitive determination than can be secured from any other sense 

 perception. 



The preceding pages may have conveyed the impression that the 

 study of physics is a stern and difficult one. While there was no 

 wish on the writer's part to magnify the difficulties of this most inter- 

 esting science, it was a definite part of his plan to show that the proper 

 teaching of physics does not consist in the acquisition by the pupil of 

 first-hand knowledge of phenomena; neither does it consist in trying 

 to implant a spirit of inductive reasoning whereby a student is led 

 to divine the great laws of nature as a discoverer; least of all is the 

 obedient following of directions set down in a manual or given by an 

 instructor the study of physics. That alone is true and successful 

 study which cultivates logical power in dealing with phenomena, gives 

 a tenacious hold upon what is known and adds at least something of 

 how the field in present possession of the science was explored and 

 occupied. 



