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Laws of Physical Science: A Reference-book

Nature volume 100, page 265 (06 December 1917) | Download Citation



THOSE who at any time have had to look up the laws of some branch of physics rapidly must have felt very seriously the absence of any pocket-book of the type so much used by engineers in which those laws were briefly and clearly stated. They will be in a position to appreciate Dr. E. F. Northrup's book, in which the principal laws are summarised. In a book which so obviously fills a gap in our literature it is perhaps a little ungrateful to point out minor defects. The contrast between the thoroughness of the section devoted to current electricity and the incompleteness and lack of unity of some of the other sections is very marked. On p. 45, for example, the author speaks first of the “force” of a musical sound, and then of the “intensity” of a sound. On p. 47 the velocity of sound is given in terms of quantities expressed in gravitational units, while on p. 51, in another formula for the velocity, tensions are expressed in dynes and masses in grains (probably a misprint for grams). On p. 61 heat energy other than translatory energy is ignored, while on p. 68 many of the general properties of isothermal surfaces and of lines of flow are given as if they held for a point source only. While in magnetism there is a partial definition of unit pole, in electrostatics there is no definition of unit quantity of electricity, and formulae are given sometimes with, sometimes without, the dielectric constant appearing. In the light section the laws of refraction include the statement that the incident and refracted rays are on opposite sides of the normal, while the laws of reflection contain no corresponding statement. Again, the relative sizes of object and image formed by a spherical mirror are stated on p. 168 as if the only possible objects and images were lines perpendicular to the axis of the mirror. In a second edition it is to be hoped that these defects will be remedied.

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