83 



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



offshore distance at sea. [IS.] 



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. 

 Dittmar'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 (q.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 Pilot 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.] 



V 2 



