curve (in which the abscissæ represent the impressed electromotive force and the ordinates the corresponding values of the current) it will be found that such a curve will not be straight, but either convex or concave to the axis of electromotive force. On describing such a curve of variation (the electromotive force rising from zero to a maximum and falling back from maximum to zero) it will be found that with certain substances the ascending and descending or outgoing and return curves coincide. I find that such substances exhibit automatic and rapid self-recovery from the effects of Hertzian waves. I have found that by employing any substance of this class as the sensitive substance of coherers or detectors for electrical disturbances, Hertzian waves, light-waves, and other radiations I can dispense with mechanical means for effecting the recovery of the coherer or detector—that is to say, these substances possess the property of rapid self-recovery.
Of the substances which give a characteristic curve, such as just described, some have the property of presenting a decreasing resistance to the passage of the electric current with an increasing impressed electromotive force, while others have the opposite property—namely, that of presenting an increased resistance as the impressed force increases. For simplicity's sake I will call the substances of the former class "positive" and those of the latter class "negative." I may according to this part of my invention use either class of substances as the sensitive substance of coherers or detectors. As examples of such substances I will mention galena, tellurium, magnesium; (these substances are positive, in the sense just described, and are self-recovering;) halogenated metals—for example, lead and tin; potassium; allotropic silver—namely, silver in a form such as can be obtained by reducing silver chlorid by zinc or by electrolysis; (these substances are all of the negative class and are all self-recovering.) Or I may use chromium, manganese, or zirconium as the sensitive agents in coherers and detectors. These substances are very sensitive and belong to the positive class, as before defined, but are possibly not self-recovering. They may, however, be used with advantage.
According to my invention I may also use ammonia-vapor or carbonic-acid gas in small proportions to stimulate the action of the sensitive agent in coherers or detectors—that is to say, to increase their sensitiveness, the gas being confined in the tube or chamber with the sensitive agent. The ammonia or carbonic-acid gas may also be used in large proportions to produce a depressing action upon the sensitive agent—that is to say, to reduce the sensitiveness thereof.
Another part of my invention has for its object to provide a novel apparatus or instrument for use in detecting or indicating light-waves, Hertzian waves, and other radiations. This apparatus when arranged for use with light-waves may be regarded as an artificial retina. By suitably modifying the arrangement, however, as hereinafter described, it may be used as a coherer or detector of Hertzian waves for the purpose of wireless or other telegraphy or for the reception of other radiations. In this apparatus or instrument a sensitive substance, positive or negative in the sense above defined and which gives a characteristic curve of the kind above described or which is made to give such characteristic curve by any of the methods of treatment above described, is employed. Both the positive and negative classes of sensitive substances when suitably disposed—as, for example, in the instrument hereinafter described—will respond to and may be caused to indicate light-waves, Hertzian waves, or other radiations by means of a galvanometer or other suitable electrical indicating or recording apparatus. In order, however, that the apparatus to which this invention relates shall work to the best advantage, it is desirable that the distortion, whether positive or negative, produced by the light-wave or other radiation shall not only be readily detected and indicated, but also that the substance shall return to its normal state upon the cessation of the impressed radiation. For this reason it is desirable to use substances having a characteristic curve of the kind above referred to or to provide means whereby said substances shall be caused to give such characteristic curve.
I will proceed to describe an apparatus constructed in accordance with this part of the invention, it being understood that I do not confine myself to the exact details of same, which may be varied without departing from the spirit of the invention.
In the accompanying drawings, Figure 1 is a diagrammatic view showing the instrument partly in longitudinal section connected up in an electric circuit with a galvanometer, as hereinafter described. Fig. 2 is a part-longitudinal section of the instrument, on a larger scale than Fig. 1, showing the contact-carrying arms, contacts, and mechanism of the instrument. Fig. 3 is a vertical section on the line a b of Fig. 2.
Referring to the drawings, 1 2 are horizontal arms of electrically-conducting material mounted upon a pivot 3 at a point intermediate between them. For this purpose the arms 1 2 each carry hinge or pivot cheeks 8 9, of insulating material. The inner extremity of each arm 1 2 is bifurcated, and in the respective bifurcations are fitted contacting pieces 4 5, of suitable positive or negative substance, sensitive to light-waves, Hertzian waves, or other radiations and giving the characteristic curve before mentioned, and thus having the property of self-recovery above described—such, for example, as the positive
