An instrument for determining through flotation the density or specific gravity of liquids and fluids. It consists of a weighted glass bulb or hollow metallic cylinder with a long stem on which the Baumé scale is marked. Dropping it into a liquid it floats in a vertical position, and sinks to a level consistent with the gravity of the fluid. =Hydrometer, Baumé.= An apparatus for testing the gravity of fluids. The zero point corresponds to the specific gravity of water for liquids heavier than water. A gauge, valuable in testing acids and other fluids used in electrical work. I =Igniter.= A mechanical hand apparatus, in which a battery, induction-coil, and vibrator are located, and whose spark, jumping across a gap at the end of a rod, ignites or lights a gas flame, blasting-powder, or dynamite. =I-H-P.= An abbreviation for indicated horse-power. =Illuminating Power.= Any source of light as compared with a standard light--as, for instance, the illuminating power of an electric light reckoned in candle-power. =Illumination.= A light given from any source and projected on a surface, per unit of area, directly or by reflection. It is stated in terms--as, for instance, the candle-power of a lamp. When speaking of an incandescent lamp we say it illuminates equal to four candle-power or it gives a light equal to sixteen candle-power. =Immersion, Simple.= Plating, without the aid of a battery, by simply immersing the metal in a solution of metallic salt. =Impulse.= The motion produced by the sudden or momentary action of a force upon a body. An electro-magnetic impulse is the action produced by the electro-magnetic waves in magnetizing a mass of soft iron and attracting to it another mass of iron or steel. An electro-motive impulse is one where the force rises so high as to produce an impulsive discharge such as that from a Leyden-jar. =Incandescence, Electric.= The heating of a conductor to red or white heat by the passage of an electric current. For example, an incandescent lamp. =Incandescent Circuit.= (_See_ Circuit, Incandescent.) =Incandescent Lamp-filament.= (_See_ Filament.) =India-rubber.= (_See_ Caoutchouc and Gutta-percha.) =Indicator-card.= The card used in galvanoscopes, volt and ampere meters, and other instruments. It is provided with a moving needle and is marked with a graduated scale. =Induced.= Caused by induction, and not directly. =Induced Current.= (_See_ Current, Induced.) =Inductance.= That capacity of a circuit which enables it to exercise induction and create lines of force. Inductance is the ratio between the total induction through a circuit to the current producing it.