tele thermometer (tel"ethermometer)

[ auxiliary needle which carries a fork at its extremity. The the fork are so placed that the primary pointer of the instrument rests between them. Thus, the motion of the pointer of the instrument is limited by the fork, and an electric contact is made when the pointer, responding to a change of temperature, touches either arm of the fork. The arms are insolated from each other, and separate wires carry the electric current from the two arms to the receiver. The two currents, therefore, distinguish rising and falling temperatures. At the receiver the current sets in motion a train of wheelwork, which moves the registering pen of a chronograph-barrel exactly one scale-division. The displacement is upward or downward according as the electric current is due to a rising or a falling temperature. Simultaneously the wheelwork plunges a metal weight into a cup of mercury, and closes an electric current independent of the first. The current thus established returns to the transmitter, and acts on a magnet whose function it is to move the auxiliary needle bearing the fork so as to bring the two arms of the fork again to equal distances from the primary needle. The apparatus is completed by an automatic interrupter, which operates after each return of the current from the receiver. The instrument is then in readine to record another differential change of temperature. This system of electrical registration at a distance is applicable to any instrument whose indications are shown by a dial and IMG:content-0048.jpg:[graphic] pointer.