Induction currents are also produced in coils of wire by the action upon them under certain conditions of a permanent magnet--as in the ordinary rotary magneto-electric machine--but these machines may be discarded from our consideration, for they are uncertain in action, painful in application, and do not admit of exact graduation. An apparatus in which both currents are combined is extremely convenient if it is so constructed that either the Voltaic or Faradaic current can be brought to the same terminals, thus avoiding the trouble of changing the conductors--a point of the greatest possible convenience when examining patients for diagnostic purposes by both forms of electricity, either in succession or alternately. [SN: The Hospital Combined Battery.] In the _Hospital Combined Battery_ (see Fig. 12), constructed from my designs, the two currents are thus united, and its details are precisely similar to those of the separate batteries, with the exception of the Dial being furnished with an additional stud lettered _Coil_. When the needle points to this stud the current from the Faradaic coil is brought into action; when it points to the numbered studs, the cells numbered thereon as in my Voltaic instrument, and when it points to “0,” both currents are shut off. [Illustration: FIG. 12. Hospital Combined Battery. A. Guard block. K. Tray for holding accessories. E. Dial plate. C. Bolt securing element board. G. Key for interrupting current. M. Hammer. F. Commutator of the poles. I, I. Binding screws for conducting wires. L, L. Hinges of element board. H. Graduator of coil. N. Electro-magnet. R. Screw regulating position of needle. D. Screw regulating spring of hammer. ] Other instruments, such as those of Stöhrer and Weiss, are excellent, and were unsurpassed until the invention and improvement of the Leclanché and other cells. But I might talk upon instruments for hours without exhausting the list; and I have felt obliged to limit myself to a description of those I believe best fitted to our requirements; but it, of course, must be understood that my further _observations will apply equally to currents of electricity furnished by any properly constructed and reliable apparatus_. [SN: Accessories of the Battery.]