FIG. 7.—WIEDEMANN'S CURRENT BREAKER.
To end our review of the scientific apparatus at the exhibition we shall merely mention Mr. Van Rysselberghe's registering thermometrograph (shown in Figs. 13 and 14), and shall then say a few words concerning two types of registering apparatus—Mr. Harlacher's water-current register and Prof. Von Beetz's chronograph.
FIG. 8.—WIEDEMANN'S BIFILAR GALVANOMETER.
Mr. Harlacher's apparatus was devised by him for studying the deep currents of the Elbe. It is carried (Fig. 15) by a long, vertical, hollow rod which is plunged into the river. A cord that passes over a pulley, P, allows of the apparatus, properly so called, being let down to a certain depth in the water. What is registered is the velocity of the vanes that are set in action by the current, and to effect such registry each revolution of the helix produces in the box, C, an electric contact that closes the circuit in the cable, F, attached to the terminals, B. This cable forms part of a circuit that includes a pile and a registering apparatus that is seen at L, outside of the box in which it is usually inclosed. In certain cases, a bell whose sound indicates the velocity of the current to the ear is substituted for the registering apparatus.
FIG. 9.—WIEDEMANN'S GALVANOMETER FOR STRONG CURRENTS.
Fig. 16 represents another type of the same apparatus in which the mechanism of the contact is uncovered. The supporting rod is likewise in this type utilized as a current conductor.
FIG. 10.—ZENGER'S DIFFERENTIAL PHOTOMETER.