Reports of the Committee on Electrical Standards Appointed by the British Association for the Advancement of Science (Google eBook)

Fleeming Jenkin
E. & F.N. Spon, 1873 - Cables, Submarine - 248 pages

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Contents

 Section 1 1 Section 2 88 Section 3 100 Section 4 114 Section 5 132 Section 6 143 Section 7 149
 Section 8 185 Section 9 225 Section 10 232 Section 11 235 Section 12 243 Section 13 246

Popular passages

Page 224 - As resistance is directly proportional to the length, and inversely proportional to the area of the cross-section, the required resistance is R = 18.7 X ||||-X |= 10.5 ohms (approx.) Ans.
Page 42 - C; and if the conductor be at all points equidistant from the pole, or, in other words, be bent in a circle of the radius k round the pole, the force is proportional to the length of the conductor (L) ; it is also inversely proportional to the square of the distance (k) of the pole from the conductor, and is affected by no other circumstances than those named. Hence we have * Vide Appendix C, § 31.
Page 45 - V, that is to say, the resistance of a conductor may be expressed or defined as equal to the velocity with which it must move, if placed in the conditions described, in order to generate a current equal to the product of the length of the conductor into the intensity of the magnetic field; or more simply, the resistance of a circuit is the velocity with which the conductor...
Page 189 - PouilletJ, established the truth of Ohm's theory shortly after the year 1830. The conception of a unit of resistance is implicitly contained in the very expression of Ohm's law ; but the earlier writers seem to have contented themselves with reducing by calculation the resistance of all parts of a heterogeneous circuit into a given length of some given part of that circuit, so as to form an imaginary homogeneous conductor, the idea of which lies at the basis of Ohm's reasoning. These writers, therefore,...
Page 84 - In the case of a soap-bubble its effect will be to cause a slight enlargement of the bubble on electrification with either vitreous or resinous electricity, and a corresponding collapse on being perfectly discharged. In every case we may consider it as constituting a deduction from the amount of air-pressure which the body experiences when unelectrified. The amount of deduction being different in different parts according to the square of the electric density, its resultant action on the whole body...
Page 130 - ... a thin brass case, which allows the coils to be plunged in a bath of water by which their temperature may be conveniently regulated and observed. Two short copper terminals project from the case and are forked at their ends, so that they may be connected with the Wheatstone's balance in the manner recommended by Professor W. Thomson, avoiding the error due to the possible resistance of connexions. The mercury standards consist of two glass tubes about three-quarters of a metre in length. " These...
Page 59 - ... show how all electric phenomena may be measured in terms of time, mass, and space only, referring briefly in each case to a practical method of effecting the observation.
Page 3 - ... definite idea in the minds of even ignorant men, and might possibly, with certain precautions, be both permanent and reproducible, whereas Weber's unit has no material existence, but is rather an abstraction than an entity. In other 'words, a metre of mercury or some other arbitrary material, might possess what we have called the first, fourth, and fifth requisite qualities, to a high degree, although entirely wanting in the second and third. Weber's system, on the contrary, is found to fulfil...
Page 163 - ... each) from a fixed mark on the roof of the instrument. The hole in the roof through which the screw-shaft passes is wide enough to allow the shaft to turn without touching it, and the lower edge of the graduated circle turning with the screw is everywhere very near the upper side of the roof, but must not touch it at any point. A second nut (c, fig. 8) above the effective nut fits easily, but somewhat accurately, in the hollow brass tube, but is prevented from turning round in the tube by a proper...
Page 40 - The absolute system is, however, not only the best practical system, but it is the only rational system. Every one will readily perceive the absurdity of attempting to teach geometry with a unit of capacity so defined that the contents of a cube should be 6¿ times the arithmetical cube of one side, or with a unit of surface of such dimensions that the surface of a rectangle would be equal to...