Abstract
THIS is another of those books in which the author does not understand the first principles of the science with which he deals. The laws of motion seem to be affording more than usual trouble to certain people just now, and most unfortunately they write books about it couched in the longest scientific terms and the most formidably accurate-looking phraseology. The author alleges, as one of the extraordinary paradoxes among the opinions of the nineteenth century, “how all bodies are supposed to persevere in their state of rest or of motion, in a straight line, unless compelled to change that state of rest or motion by the impression of some force on them; and how, in opposition to this law, the planets become accelerated and retarded in their orbits without such adequate impression of force; also how bodies initially projected at the surface of the earth, fall by the force of gravitation with velocities uniformly accelerated, and how the planets similarly projected descend towards the sun with velocities comparatively equal throughout the entire duration of their revolutions.”We need hardly remind the reader that these conclusions, so far from being in any way in opposition to the law of motion stated by the author, are in complete harmony with that law, and, as was demonstrated by Newton, follow from it on the hypothesis (to give it no higher name) of gravitation. The author at least might have observed, in comparing the case of the stone and of the planet, that the direction of the force on the former is unaltered, while that of the force on the latter is continually changing.
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