153 



connecting to an ordinary bell or sounder for use in the 

 lecture room. [10, 19.] 



Section Cutter. A microtome (q.v.). [3, 4, 10, 20, 22, 26.} 



Sectoral Compass. A special form of drawing compass. [2, 15, 

 27.-] 



Seger Cones or Pyroscopes. A series of fusible clay cones which 

 melt at various definite temperatures ranging from 590 C. 

 to 2,000 C., and can thus be used as temperature indicators. 

 [17.] 



Seismograph. An apparatus for recording and measuring the 

 direction, duration, and force of earthquakes and earth 

 tremors. See also Vibration Recorder. [13, 17, 21, 26.] 



Seismometer. See Seismograph. [4, 13, 17, 21, 26, 27. \ 



Seismophone. An instrument for distinguishing and locating 

 subterranean sounds such as that of flowing water, subter- 

 ranean explosions, etc. 



Seismoscope. A vibration instrument for indicating earthquakes, 

 earth tremors, etc. [17.] 



Selenite Stage. An accessory used in the microscopic examina- 

 tion of chemical and geological specimens under polarised 

 light. It usually consists of a thin section of selenite or 

 gypsum suitably mounted on glass. 



Selenite Stage, Barker's. A brass stage in which mounted 

 selenites of different wave-length can be rotated below a 

 microscopic specimen under polarised light. 



Selenite Stage, Mica. A brass stage containing three selenites of 

 different wave-lengths, any one of which can be slid over a 

 disc of mica, the latter being capable of rotation. For use 

 with polarised light in microscopical examination. 



Selenium Eye. A device for making a model eye blink by the 

 action of light. [26.] 



Selenotrope. A model showing the phases of the moon. 



Semaphore. A signalling device employing moving arms or 

 plates. [13, 15, 16, 28.] 



Sematrope. An instrument for signalling by reflecting the rays 

 of the sun in different directions. 



Semicircumferentor. A simple mining surveying instrument 

 much used for surface work. [13, 15, 17, 21, 24, 25, 27.] 



Sensitometer. See Actinometer. [26.] 



Separable Socket Thermometer. See Thermometer. [13.] 



Set-Square. An instrument used by draughtsmen in combina- 

 tion with a tee-square for drawing perpendicular lines or 

 those of specified angles. [2, 5, 6, 13, 15, 17, 20, 21, 24, 25, 

 26, 27, 28.] 



Sextant. An instrument for measuring angular distances 

 between objects, used especially at sea for ascertaining the 

 latitude and longitude by determination of the altitude of 

 the sun or stars. It is constructed on the same optical 

 principle as Hadley's quadrant (q.v.). [2, 5, 6, 9, 10, 13, 

 15, 16, 17, 20, 21, 25, 26, 27, 28.] 



