Nikola Tesla Patents
424 8 former. The scheme of connections is, in the main, that of a Wheatstone bridge, the four branches of which are formed by the sensitive device a and resistances L, L' and L", all in a continuous manner, or at least by very small steps. The condenser C', which is generally made of considerable capacity, is connected to two opposite points of the bridge, while a battery B, in series with a continuously adjustable, noninductive resistance r' is connected to the other pair of opposite points as usual. The four resistances included in the branches of the bridge, namely a, L, L' and L" are of a suitable size and so proportioned that under normal conditions, that is, when the device a is not influenced at all or only slightly by the disturbances, there will be no difference of potential or, in any case, the minimum of the same, at the terminals T and T' of the condenser. It is assumed in the present instance, that the disturbances to be investigated or utilized are such as will produce a difference of electric potential, however small, between two points or regions in the natural media, as the earth, the water or the air, and, in order to apply this potential difference effectively to the sensitive device a the terminals. of the same are connected to two plates P and P' which should be of as large a surface as practicable, and so located in the media that the largest possible difference of potential will be produced by the disturbances between the terminals of the sensitive device. This device is, in the present case, one of familiar construction, consisting of an insulating tube, which is indicated by the heavy lines in the drawing and which has its ends closed tightly by two conducting plugs with reduced. extensions upon which bear two brushes bb, through which the 14. [This page retyped from microfilm for better readability - Ed.]
