Coherer without Filings.
Were it not for reasons, such as difficulty of decoherence, the metal filings might be dispensed with and two rods of metal placed in light contact. The construction of the coherer reminds one very much of the microphone, a satisfactory coherer having been made out of the old "nail microphone," four wire nails being placed crossing one another in the battery circuit, in one case acting as a sound transmitter, whence the name; in the other as a coherer.
Aluminium Coherer.
Aluminium, a metal which has steadily grown into favor, and which is now readily obtainable, can be made to serve in the present apparatus in place of nickel both as to electrodes and filings. It is advisable, however, to use aluminium electrodes of slightly larger diameter than those of other metals.
Steel Ball Coherer.
A recent writer has recommended the use of balls of steel, such as are used in ball bearings, such, however, not to exceed ⅜ inch diameter. Such a coherer would take the form of an upright glass tube, with electrodes exerting pressure on a series of four or more steel balls. Decoherence here becomes difficult, and mention is but made of it to show the variety of forms which this important little article may assume.
Coherers are adjusted by advancing or receding the electrodes, altering the quantity of the filings, etc. There exists but little difficulty in operating coherers; considerable latitude is permissible as to adjustment, size, character, etc. There does not seem so much difficulty in obtaining sensitiveness as in guarding against external electrical disturbances. Wings or vanes of thin sheet metal are sometimes attached to the metal ends or electrodes of the coherer for purposes of adjustment, their size and capacity being determined by experiment. It is best that they present no sharp angles, but be of a disc, or spherical, form, the better not to dissipate energy.
The Oscillator.
This is the name given the contrivance at the ends of the discharger, D being the point at which the electrical oscillations, or waves, are radiated.