83 



Distance-Finder, Smith's. An instrument for calculating the 



* offshore distance at sea. [15.] 



Distance-Finder, Stewart's. An optical instrument, consisting of 



a moveable prism plate, a small sighting telescope, and a 



xylonite diagram plate ; used for ascertaining the distance 



|^ of an object and for keeping a ship on station with another. 



[8, 13. IS.] 



Distance-Meter. A rangefinder or telemeter. [2, 13, 15, 17, 20, 

 21, 27.] 



Distance-Recorder, Forbes's. A form of ship log. 



Dittrnar's Gas Analysis Apparatus. See Gas Analysis Apparatus. 

 [17.] 



Divider. An instrument for dividing lines, describing circles, 

 etc. A form of compass. [2, 5, 6, 9, 13, 15, 16, 17, 20, 21, 

 24, 26, 27, 28.] 



Divider, Hair. A pair of dividers, one of the legs of which is 

 provided with a set-screw and spring, admitting of a very 

 fine adjustment between the two points. [2, 15, 17, 21, 24.] 



Dividing Engine. A machine for accurately dividing the linear 

 or circular scales of surveying, astronomical and other 

 instruments. [4, 6, 10, 13, 17, 18, 19, 21, 27.] 



Dividing Machine. See Dividing Engine. [4, 10, 13, 15, 17, 18, 

 19, 21, 24, 27.] 



Dolezalek Quadrant Electrometer. See Electrometer. [4, 19.] 



Dosimeter. A drop meter for measuring a certain number of 

 drops. [6.] 



Dotting Pen. A drawing pen having a toothed wheel inserted 

 between the nibs for producing a dotted or spaced line, for 

 the use of draughtsmen. [2, 5, 13, 15, 17, 20, 21, 24, 26, 27.] 



Double-Coil Galvanometer. See Galvanometer, Thomson. [4, 

 16] 



Double-Image Prism. See Prism. [2, 3, 13, 20, 22.] 



Double Sextant. See Sextant. [2, 10, 13, 15, 20, 21, 26, 27, 28.] 



Doublet Magnifier. A magnifying glass (g.v.) composed of 

 two lenses, sometimes cemented together and sometimes 

 separated. [1, 2, 3, 10, 17, 20, 21, 22, 26.] . 



Dough-Testing Thermometers. See Thermometer. [5, 6, 13, 15, 

 20.] 



Draught-Gauge. A manometric or other pressure gauge for the 

 measurement of pressures slightly above or below atmo- 

 spheric, as chimney draught, etc. See also Manometer 

 and Pitot Tube. [4, 5, 16, 17.] < 



Draught-Gauge, Differential. An instrument for measuring the 

 varying draught in steam boilers, coke oven plants, etc. 

 [6, 16, 17.] 



Drawing-Board. A rectangular board of pine wood, specially 

 framed to prevent warping, and having a true surface and 

 edges for the use of draughtsmen. [2, 5, 6, 13, 15, 17, 20, 

 21, 24, 26, 27.] 



Drawing-Eyepiece. See Eyepiece. [2, 3, 10, 17, 20, 22, 26.] 



r 2 



