An international system of electro-therapeutics : for students, general practitioners, and specialists . n to beanalogous to the density of ordinary matter; and this magnetic perme-ability, which is simply the ratio in which a magnetic field is strength-ened at any point by the presence of that substance instead of air at the ELECTRO-PHYSICS. A-63 point, is readily determined by proper methods. It is usually denotedby ft. Thus, the foregoing formula of Newtons becomes, for the case ofelectro-magnetic waves, Now, the velocity of light in various substances is deduced from theirrefractive indice
An international system of electro-therapeutics : for students, general practitioners, and specialists . n to beanalogous to the density of ordinary matter; and this magnetic perme-ability, which is simply the ratio in which a magnetic field is strength-ened at any point by the presence of that substance instead of air at the ELECTRO-PHYSICS. A-63 point, is readily determined by proper methods. It is usually denotedby ft. Thus, the foregoing formula of Newtons becomes, for the case ofelectro-magnetic waves, Now, the velocity of light in various substances is deduced from theirrefractive indices, and so we can test the agreement between these twovelocities. This agreement, though not perfect, is close enough to form aconvincing proof of the theory. 97. Vibrations constituting an Electro-magnetic Wave,—Whena current is started in a conductor, ~Yb, it immediately sets up a fieldof magnetic force, and we saw that the lines of force of this field werecircles inclosing the current (§38). Now, it is proven that this magneticinfluence of the current spreads out not instantaneously, but with a. measurable velocity, namely, that of light. We may represent this bythinking of the circles widening out with that speed in all circles are always perpendicular to the radial direction, such as M M,in which they are carrying the magnetic influence of the current. Now,this direction is the direction in which the waves travel, the front of thewave being, of course, at right angles to the direction in which it istraveling. Hence, the lines of magnetic force lie in the front of theadvancing waves. Again, the growing current has an electrical influence such that,wherever it finds a conductor, it will set up a (momentary) current in itin a direction opposite to itself; or, at a point where it finds a dielectric,it will set up a strain in the dielectric, the direction of the strain beingopposite to that of the original current. This direction, also, is perpen-dicular to the
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectuterus, bookyear1894
