Sir William Armstrong’s Electric Machine is a mode of obtaining electricity by moist steam. The design is Armstrong’s, and Professor Faraday subsequently went into all the conditions to produce the “fluid” by the friction of steam. The machine was something like a small boiler supported on glass legs. A row of nozzles was fixed upon the escape pipe so as to create a great velocity and friction in the escaping steam. Round the nozzles was a box of cold water, for that fluid was found necessary for the production of electricity as demonstrated by Professor Faraday. The steam rushed against a row of points attached to the prime conductor of an electric machine, and the electricity of the steam was thus given off to the conductor. There are many other forms of electric machines, but it will serve no purpose to detail them. [Illustration: Fig. 214.—Discharging rod.] The _Electric Battery_ (_see_ fig. 206) is formed by a collection of Leyden jars. The inside and outside coatings are connected in a box divided into partitions lined with tinfoil. The rods of the jars are also connected, as in the illustration, by brass rods, and when this battery is charged people should be careful how they handle it, for a shock may be produced which would cause serious injury, if not death. The battery can be charged from the machine by a chain fastened to the central ball, while a second chain connects the exterior of the box and all the outside of the jars, by means of the handle, to the ground. When electricity is at rest it is termed “static electricity,” and when in motion “dynamic” electricity. The latter treats of electric currents which can be sent through wires or chains. We can keep this current moving by means of a machine, and the battery called a Voltaic battery, from Volta. We will describe it presently. Electric currents can be measured, for they may be of different strengths according to the battery, and they are measured by the GALVANOMETER. Electricity can therefore be transferred and carried by the conducting substances, and much heat will be engendered as the “electric fluid” passes along a wire. Lightning frequently fuses bell-wires as it passes, and when we touch upon Galvanism or Dynamical Electricity we shall hear more about it. By the Electric Machine we can obtain some very powerful currents of electricity; we can produce many pleasing effects, and perform a number of experiments, such as making balls or figures of pith dance, and several other easy and entertaining tricks, which will be found in books more specially devoted to the entertainment of young people. [Illustration: Fig. 215.—Leyden Jar.]