In comparison with so-called coherers, those depending upon the changes in the magnetisation of iron by electrical oscillations certainly have an advantage, because this is a process which requires the application of alternating electric currents decreasing in strength for a certain time; and it is found, therefore, that the magnetic receivers do not require to be associated with such a stiff or irresponsive resonant circuit to confine their indications to oscillations or waves of one definite period, and that they lend themselves much more perfectly to the work of "tuning" or syntonising stations than do those kumascopes depending upon the contact or coherer principle. We may then glance at the alternative solutions of the problem offered by other investigators. M. Blondel has proposed to effect the syntonisation of two stations, not by syntonising the receiver for the exceedingly high-frequency oscillations of the individual electric waves, but to syntonise it for the much lower frequency, corresponding to that of the intervals between the groups of waves. Thus, for instance, if an ordinary simple transmitting aerial is set up, the production of sparks between the spark balls results in the emission of short trains of waves, each of which may consist of half a dozen or more individual waves, the time of production of the whole group being very small compared with the interval between the groups. M. Blondel proposes, however, to syntonise the receiver, not for the high-frequency period of the waves themselves, which may be reckoned in millions per second, but for the low-frequency period between the groups of waves, which is reckoned in hundreds per second. Thus, for instance, if sparks are made at the rate of fifty or a hundred per second, they can be made to actuate the telephone receiver and so produce in the telephone a sound corresponding to a frequency of 50 or 100; in other words, to make a low musical note or hum. This continuous sound can be cut up, by means of a key placed in the primary circuit of the transmitting arrangement, into long or short periods, and hence the letters of the alphabet signal.