Electrical oscillations of low frequency and their resonance

THE sensitiveness of the telephone for exceedingly small alternating currents is well known. It is probably as great as that of the most delicate Thomson galvanometer for direct currents. Just as this instrument, so the telephone is especially suited to zero-methods. But the telephone does not enjoy that popularity in the precision room which its direct current rival, the Thomson galvanometer, enjoys, although the field of physical research in which alternating currents must necessarily be employed is very extensive indeed. The fault lies with our alternating cnrrents and not with the telephone. The alternating CUl'l'ents which the ordinary induction coil as employed in physical laboratories produces is far from being a simple hal" monic current. The consequence is that in very many cases the zero method, for which the telephone is especially suited, has to be abandoned, and the minimum method substituted for it, which, of course, is a poor Sll bstitution. Being engaged in a research in which I had to employ alternating currents I tried, for reasons just given, to devise some method of producing simple harmonic currents of constant frequency, the freqnency to be easily and very accurately determinable. The following is my solution of this interesting problem: