Page:Popular Science Monthly Volume 45.djvu/529

Rh 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 matter for the novice to join the throng.



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 beginner, or one with no preconceived ideas on the subject, there would perhaps appear nothing surprising, but to an older student, 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 college 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 conservative 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, electrostatics, 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 