^{page 612 note *} The self-induction coefficients of the primary and secondary of a middling-sized Ruhmkorff's coil, when expressed in the same unit, run to from ·01 to ·1, and from 50 to 100 respectively.

^{page 615 note *} Strictly speaking, an iron core is inadmissible in measurements with the telephone, because it acts as a neighbouring circuit, and introduces disturbances that cannot be compensated in a simple manner. I have found, however, in practice that, when the core is made of thin wires well insulated from one another, these residual effects are so small as not to interfere with the results, where the utmost nicety is not required.

^{page 616 note *} It would be easy to work out the general theory with more detail, much in the way that a system of conductors is treated when induction is neglected. (See Maxwell's, “Electricity and Magnetism,” or article “Electricity,” Encyclopædia Britannica, vol. viii. p. 43)Google Scholar.

^{page 625 note *} See Aron, Wied. Ann. N.F., vi. p. 403.

^{page 625 note †} On this subject see two very interesting articles by Lord Rayleigh, Phil. Mag., 1869, p. 8, and ser. 5, vol. iii. p. 46 (1877).

^{page 626 note *} The compensation according to theory is exact for one particular note only.

^{page 627 note *} Phil. Mag., May 1880.

^{page 628 note *} It is much to be desired that some of the above observations should be repeated by some one with a better ear for pitch than mine. I believe that very close accordance between theory and experiment would be brought out. I have not pushed either the theory or the experiments so far as I might have done, on account of my comparative obtuseness in the matter of pitch.

^{page 633 note *} To avoid all possibility of misconception, I may repeat that the above table is calculated on the supposition that the amplitude of the disturbing electromotive force is independent of n. The comparison for the present purpose goes by horizontal rows.

If it be desired to compare vertically, and an approximation to the case of a telephone sender be contemplated, then the values of ξ₁, ξ₂, ξ₃, &c. must be multiplied by the respective values of n ². Thus the values of ξ₁, become 11, 22, 25, 25, 25, 25, 25, those of ξ₂,, 15, 45, 60, 62, 62, 62, 62; so that the quality (i.e., the ratios of the intensities of the tones of different pitch) would be little altered by telephonic transmission in the two cases, if we except very low notes. This agrees with the general conclusions of Helmholtz (Telephon und Klangfarbe, Wied. Ann. N. F. v. p. 448).

The same remark does not apply to the case where a condenser is introduced, a case not contemplated of course in Helmholtz's theory. It is one of the points of the above investigation to have (I hope) made clear the exact nature of this peculiar class of exceptions to the general statement that the telephone does not greatly alter the quality of the transmitted sounds. In connection with this matter I may refer to an exceedingly interesting little paper by Hagbnbach, Wied. Ann. N. F. vi. p. 403.