MODERN VIEWS AND PROBLEMS OF PHYSICS. 511 



they will respond to an imitation of their notes. We have seen 

 that when under way they constantly chirp and call, and when 

 we take into consideration their aural power and their abundance 

 in highways of migration, it is probable that at no time during 

 the night is a bird out of hearing of its fellow-travelers. The 

 line of flight once established, therefore, presumably by the older 

 and more experienced birds, it becomes a comparatively easy mat- 

 ter for the novice to join the throng. 



MODERN VIEWS AND PROBLEMS OF PHYSICS. 



BY DANIEL W. HEEING, C. E., 



PROFESSOR OF PHYSICS IK THE UNIVERSITY OF THE CITY OF NEW YORK. 



A GOOD idea of the generally accepted views upon a science 

 in all its branches may be obtained by inspecting standard 

 text-books on the subject, for such works are not likely to meet 

 with the approval of scholars, and especially of professors, if they 

 present views that are antiquated in form or palpably erroneous 

 in statement. 



In thus approaching a modern text-book of physics, to a be- 

 ginner, or one with no preconceived ideas on the subject, there 

 would perhaps appear nothing surprising, but to an older stu- 

 dent, say the college alumnus of fifteen years' standing who has 

 not kept abreast of the science, the change would be striking. 

 He would probably be impressed as much by the absence of 

 things he had thought inseparable from the subject as by the 

 presence of things of which he heard little or nothing in his col- 

 lege course. An illustration of this may be seen in a very recent 

 book of the kind named.* In its general tone it is similar to that 

 adopted about ten years earlier in the masterly presentation of 

 the Principles of Physics, by Prof. Daniell, but it is less conserva- 

 tive than that work. A glance at the headings gives the keynote 

 of the whole treatment. After a brief discussion of kinematics 

 and dynamics, mass physics is further divided into work and 

 energy, attraction and potential, properties of matter, energy of 

 mass vibration, sound. Then physics of the ether has energy of 

 ether vibration, radiant energy, energy of ether stress, electro- 

 statics, energy of ether vortices, magnetism, energy of ether 

 flow, electro-kinetics, electro-magnetic character of radiation. 



There is not an allusion to the old familiar " simple mechanical 

 powers " ; there is no mention of light or optics as a branch of 

 physics; sound, heat, electricity, and magnetism are only ap- 



* Barker's Advanced Physics. 



