152 



Scioptic Ball. The lens of a camera obscura (q.v.). [20, 26.] 



Sciopticon. A magic lantern (q.v.). [2, 17, 26.] 



Sclerometer. An instrument for determining with accuracy the 



hardness of a mineral. 

 Scotograph. An instrument for writing in the dark or without 



seeing. 

 Scotoscope. An instrument that discloses objects in the dark 



or in a faint light. 

 Screen, Filter. See Filter (Light). 

 Screw, Endless Tangent. A tangent screw acting on a continuous 



thread cut on the limbs or arc of an instrument, giving an 



endless motion of the screw. [13, 15.] 

 Screw, Endless Tangent, Reeves 's. An endless screw for use on 



sextants and theodolites. [13. 21.] 



Screw Gauge Calliper. A form of callipers (q.v.) with micro- 

 meter screw for the measurement of screw gauges and other 



small diameters or thicknesses. 

 Screw-Jack Apparatus. For experiments on the efficiency of a 



screw-jack. [19] 

 Screw-Measuring Machine. For accurately determining pitch, 



diameter, angle, etc., in screws. [2, 4, 22, 23.] 

 Scribing Iron. An implement for scribing the marks on timber. 



[21.] 

 Searcher. (i) An instrument for examining the bore of a 



cannon to detect cavities. (2) A dissecting instrument. [20.] 

 Searchlight. A light with lenses or mirrors to produce a 



powerful beam of light. [7.] 

 Searle's Apparatus. An apparatus for the determination of 



Young's modulus of wires and deviations from Hooke's 



Law. Two wires of the same material are used, their ends 



being connected by a sensitive level with a micrometer 



screw, so that the extension of one of the wires under 



varying load can be measured. [4, 8, 19.] 

 Searle's Apparatus. An apparatus for determining Newton's 



coefficient of restitution, and for finding the change of 



energy and momentum on impact. [4, 19.] 

 Searle and Pye's Revolving Table and Lens System. For the 



determination of the focal length of lens system by the 



nodal point method. [19] 

 Searle's Simple Torsion Balance. For measuring the surface 



tension of a soap film or of any clear liquid. [19.] 

 Searle's Total Reflection Apparatus. For finding the refractive 



index of a liquid by the method of total internal reflection. 



See also Refiractometer. [19.] 

 Sea Surface Temperature Thermometer. See Thermometer. 



[6, 13, 15, 17, 21, 28.] 

 Sea Wave Counter. An instrument for counting the number of 



sea waves breaking on a coast. [4] 



Seconds Pendulum. A pendulum of which the period of oscilla- 

 tion is one second, with electrical contacts arranged for 



