io8 



Indicator, Engine. An instrument for measuring the horse- 

 power of a steam or internal combustion engine. It consists 

 of a cylinder having a piston attached to a coiled spring. 

 A pencil is attached to the piston rod and describes a 

 diagram upon a card or paper fixed on a cylindrical drum 

 which vibrates horizontally with each stroke of the engine. 

 The diagram indicates the varying steam pressure during the 

 stroke. [13, 15, 16. 24.} 



Indicator, Gas Leak. An instrument for locating coal gas leaks 

 and detecting the presence of sewer gas, after-damp, etc. 

 [4, 5, 17, 21.] 



Indicator, Gradient. An instrument for indicating the up or 

 down gradient of an aeroplane or motor-car. [6, 15, 16, 17.] 



Indicator, Gravity. An instrument used for the experimental 

 verification of the laws of falling bodies. The falling body 

 generally consists of a blackened glass plate, on which a 

 style attached to a vibrating tuning fork, whose frequency 

 is known, marks a wave curve, from which the time of falling 

 through a known distance can be deduced. 



Indicator, Tabor. A form of engine indicator for testing high 

 speed engines, etc. 



Indicator Telegraph. An electric telegraph in which the signals 

 are given by the deflections of a magnetic needle. [15.] 



Indigometer. An instrument for ascertaining the strength of 

 an indigo solution, as in volumetric analysis. 



Indiscope. A form of ophthalmoscope (q.v.). 



Induction Balance. An instrument for the eradication of 

 induction currents in telegraph lines. [4.] 



Induction Coil. An apparatus for producing induced electrical 

 currents of great intensity. The essential features are : a 

 central core of soft iron, surrounded first by a coil of thick 

 insulated wire, called the " primary," and then by a longer 

 coil of very thin insulated wire, called the " secondary " ; 

 a condenser consisting of alternate layers of tin foil and 

 paraffin wax coated paper, and a means of interrupting the 

 current in the " primary." thus creating induced currents in 

 the " secondary." [4.] 



Inductiphone. A sounding instrument in which vibrations 

 transmitted by the primary are reproduced by a plate and 

 membrane. [4.] 



Inductometer. An instrument or apparatus for ascertaining the 

 force of electrical induction or for comparing the specific 

 inductive capacities of various substances. [4.] 



Inflammable Gas or Vapour Detector, Redwood. An instrument 

 for detecting and accurately measuring small percentages 

 of inflammable gases or vapours. [13, 15.] 



Ingram and Stopfer's Oil-Tester. For lubricating oils. 



Inside Calliper. An instrument for the measurement of the 

 diameter of holes in metalwork, etc., generally reading by 

 vernier to 1-1,000 in. See Callipers. [20, 25.] 



