8 7 



Electrometer, Dolezalek Quadrant. An electrometer in which a 

 light needle or vane, usually of aluminium, is suspended, 

 when in use, in the geometrical centre of quadrant shaped 

 metal plates. Opposite pairs of quadrants are connected 

 and charged to the same potential, and the deflections of 

 the " needle " are observed by means of a reflecting mirror. 

 [4, 19.} 



Electrometer, Laby String. An electrometer in which the moving 

 system is a silvered glass or quartz fibre, stretched lightly 

 between and parallel to two metal plates charged to different 

 potentials. [4.] 



Electrometer, Thomson's Quadrant. A quadrant electrometer of 

 similar type to the Dolezalek electrometer (q.v.). [16, 21.] 



Electrometer, Universal Portable. A type of gold-leaf electro- 

 meter designed by Mr. C. T. R. Wilson, in which the gold- 

 leaf hangs within an inner case which is maintained at a 

 suitable potential by means of a quartz Leyden jar. The 

 instrument will measure very small as well as higher 

 potentials. [4.] 



Electrometer, Wilson-Kaye. A sensitive electrometer in which 

 a gold leaf is attracted towards a charged plate, and the 

 resulting deflection of the leaf, which is observed by means 

 of a microscope, gives a measure of the potential to which 

 the leaf has been charged. [4.] 



Electropeter. An instrument used to change the direction of 

 electric currents ; a commutator. 



Electrophone. An instrument for producing sound by electric 

 currents of high tension. By means of twin receivers 

 placed to the ears operatic performances, etc., at a distance 

 may be heard. 



Electrophorus. An instrument for exciting electricity and 

 repeating the charge indefinitely by induction. It consists 

 of a flat cake of resin, shellac, or ebonite upon which is 

 placed an insulated plate of metal. [19.] 



Electrophotometer. An instrument for measuring the intensity 

 of light by means of electricity. See also Photometer. 



Electropyrometer. An instrument for measuring high tempera- 

 tures by means of electrical effects such as change of 

 resistance or thermoelectric effects. See Pyrometer. [1.] 



Electroscope. An instrument for demonstrating the sign and to 

 some extent the magnitude of an electric charge. [13, 



19, 26.] 



Electro Slide-Rule. See Slide-Rule. [15.] 



Elliott Air-Speed Indicator. A speed instrument for aeroplanes. 



Ellipse. A device for drawing the figure of an ellipse. [15, 17, 



20, 27.] ' 

 Ellipsograph. An instrument for drawing ellipses. [6, 20, 21.] 

 Elliptic Compasses. See Compasses. [2, 6, 13, 17, 20, 21. 27.] 

 Elliptic Curves. See Curves. [2, 6, 13, 15, 20, 21, 24, 27.] 

 Elliptograph. See Ellipsograph. [21.] 



