In time, no doubt, the investigators will find the right quality for each disease, and learn how to apply it. Thus, electricity, that most alluring thing which, in itself, cannot be seen, and is of such a character that it cannot even be defined in terms which will suit the exact scientific mind, is daily bringing new wonders for our investigation and use. It is, indeed, a study which is so broad that it has no limitations, and a field which never will be exhausted. THE END GLOSSARY OF WORDS USED IN TEXT OF THIS VOLUME Acid. Accumulator material is sulphuric acid, diluted with water. Active That part of the material in accumulator plates Material. which is acted upon by the electric current. Accumulator. A cell, generally known as a storage battery, which while it initially receives a charge of electricity, is nevertheless, of such a character, owing to the active material of which it is made, that it accumulates, or, as it were, generates electricity. Aerial Wire, The wire which, in wireless telegraphy, is carried or Conductor. up into the air to connect the antennæ with the receiving and sending apparatus. Alarm, Burglar. A circulating system in a building, connected up with a bell or other signaling means. Alloy. A mixture of two or more metals; as copper and zinc to make brass; nickel and zinc to form German silver. Alternating Current. A current which goes back and forth in opposite directions, unlike a direct current which flows continuously in one direction over a wire. Alternation. The term applied to a change in the direction of an alternating current, the frequency of the alternations ranging up to 20,000 or more vibrations per second. Amber. A resin, yellow in color, which when rubbed with a cloth, becomes excited and gives forth negative electricity. Ammeter. An instrument for measuring the quantity or flow of electricity. Ampere. The unit of current; the term in which strength of the current is measured. An ampere is an electromotive force of one volt through a resistance of one ohm. Annunciator. A device which indicates or signals a call given from some distant point. Anode. The positive terminal in a conducting circuit, like the terminal of the carbon plate in a battery. It is a plate in an electroplating bath from which the current goes over to the cathode or negative plate or terminal.