79 



Davis-Stokes Field Gunnery Slide-Rule. See Slide-Rule. [21.] 

 Day and Night Telescope. See Telescope. [3, 5, 8, 9, 10, 13, 15, 



16, 17, 20, 26, 27, 28.] 



Dead-beat Centre-Seconds Clock. A clock with electric contacts 

 and sounder to facilitate counting the number of seconds 

 when timing experiments. [10, 13, 17, 19.] 



Debuscope. A modification of the kaleidoscope invented by 

 M. Debus. 



Declination Compass. An instrument by which the magnetic 

 declination of any place may be measured when its astro- 

 nomical meridian is known. See also Compass. [13, 15, 16, 



17, 20, 21, 25, 27.] <-{ 

 Declinometer. See Declination Compass. [13, 17, 21, 25, 27.] 

 Deep-Sea Thermometer. See Thermometer. [6, 13, 15, 17, 20, 21.] 

 Deflagrator. An instrument for producing intense heat. It 



was generally a form of the voltaic battery. 



Deflectometer. Askenasy's apparatus for measuring the deflec- 

 tion of a bridge under a passing load. [21.] 



Deflector. An instrument in use on board ship for comparing 

 the magnetic directive force on different courses. [13, 15, 16.] 



Deflector, Kelvin. An instrument used in correcting or adjusting 

 the magnetic compass on vessels when bearings of land- 

 marks or heavenly bodies are not available. The instrument, 

 which was designed by Lord Kelvin, gives a measure of the 

 directive force on the compass when the ship is on various 

 courses. It consists of a magnet of adjustable magnetic 

 moment, fitted for application to the compass bowl and to 

 revolve about the compass centre, the magnetic moment 

 of the deflector magnet being indicated empirically on the 

 scale. [16.] 



Delezenne's Circle. An apparatus for showing induced currents 

 produced by rotation of a coil in the earth's magnetic field. 



Delineator. A perambulator or geodetical instrument on wheels 

 with registering devices for recording distances between 

 points on the earth's surface. [13, 27.] 



Delineator, Lenthall's. An instrument for solving many problems 

 in dead reckoning in navigation, without the use of books 

 or tables. [13.] 



De Lisle Reflecting Clinometer. See Clinometer. [2, 6, 13, 15, 17, 

 21, 24, 25, 27.] 



Denii-Circle. An instrument for measuring and indicating 

 angles. It resembles a protractor. [13, 16, 20, 21.] 



Dendrometer. An instrument for determining the height and 

 diameter of trees, [15, 17, 21.] 



Densimeter. An apparatus for ascertaining the specific gravity 

 of a liquid. [4. 13, 15, 17, 21.] 



Densimeter, Recording. An instrument giving a continuous 

 record of the density of a liquid, and thereby the varying 

 strength of acid or alkaline solutions in chemical processes, 

 etc. [4, 13, 21.] 



