We give a description of a meter we made in June, 1883.  You will find a cross section of the meter and also a printed dial we had made at the time.  We called it an ampere register, but no doubt we would give it a better name to-day.  The meter consisted of a glass tube, c, both ends of which were fitted into two bent pieces of piping, D and F, as shown.  Through these bent tubes, D and F, passed the wires, a and b, which were connected to the binding posts, A and B. The part of the wire where it passed into the tubes was well insulated.  At the ends, a’ and b’, was connected the coil, R, which consisted simply of a few turns of copper wire whose diameter was less than the leading wires, a and b.  To the tube, D, was attached a square tube, E, which had a little opening at the top so as to permit a small undershot wheel, I, to revolve freely.  This undershot wheel was well pivoted and constructed very light.  To the axis of this wheel was connected another system of wheels with indicators, as shown, J. Now the tubes, E and F, were connected to a reservoir, G. This reservoir consisted of a square tank, in the inside of which were soldered in an alternating manner square sheets of copper as shown in the drawing, g g’ g’’ g’’’ ...  These sheets acted as diffusers.  These plates or sheets presented a very large surface.  On the outside of the tank, G, were also diffusers, h h’ ... arranged all round and presenting an appearance as if two books were open so as to form a square with their covers, the leaves being the diffusers.  The diffusers on the outside were at right angles to those inside.

[Illustration:  CROSS SECTION OF JEHL AND RUPP’S CURRENT METER.]

The action of the meter was thus:  When a current passes through the coil, R, it heats the liquid at the place, thus causing a circulation, the warm liquid ascending while the cold liquid descends as shown by the arrows.  This circulation causes the undershot wheel to revolve, and its revolutions are registered by the clockwork.  The stronger the current, the more the heat, and thus the more rapid the circulation.  The warm liquid once in the tank, which is of a reasonable size, will impart its heat to all the diffusers.  The surface of the glass tube, etc., is very small in comparison to the surface of the tank.  It will be seen that the function of this apparatus is independent of the outward temperature, for the motion of the liquid is due only to that heat which is generated by the current.  When the current does not pass, it is evident that the liquid, at whatever temperature it may be, does not circulate, as all parts are of the same temperature; but the moment the current passes, a difference is produced, which causes a circulation in proportion to the current.  We may mention that we tried various liquids, and give preference to pure olive oil.  It will also be seen that this meter is good for alternating currents.  In conclusion, we may remark that the tests we made gave satisfaction, and we wanted to publish them, but that Mr. Jehl was called away to fit up the Edison exhibit in the Vienna exhibition for the Societe Electrique Edison of Paris.  After the exhibition we began our work upon our disk machine, and had almost forgotten our meter.  The whole apparatus is mounted on a base, K.