129 



Octant. An instrument for measuring angles ; it resembles a 



quadrant or sextant in principle. The eighth part of a 



circle. [10, 13, 15, 16, 21, 28.] 

 Ocular. The eyepiece of a telescope, microscope, or other optical 



instrument. [1, 2, 3, 9, 10, 15, 20, 21, 22, 26.] 

 Odograph. An apparatus for measuring the length and rapidity 



of a man's stride in walking. [13, 21.] 

 Odometer. An instrument for measuring distances. A wheel 



used by surveyors which registers the miles and rods 



traversed. [13, 17, 21, 26, 27.] 

 Odontograph. An instrument for marking or laying off the 



teeth of gear wheels. [15, 21, 24.] 

 Oenometer. A form of hydrometer (q.v .} adapted to determine 



the alcoholic strength of wines. [13, 21] 

 Officer of Watch Telescope. See Telescope. [2, 3, 5, 9, 13, 15, 



16, 17, 20, 21, 23, 24, 25, 26, 27, 28] 

 Offset Square Staff. A rod usually ten links long and divided 



into ten equal parts. Used in measuring offsets. [5, 6, 13, 



15, 17, 21, 26, 27.] 

 Offsets. Short scales for laving off the offset distances on a 



plan. [2, 5, 6, 13, 15, 17, 21, 24, 25, 26, 27.] 

 Offsetting Staff. A wooden staff divided into links for measuring 



distance on either side of the survey line. [5, 6, 13, 17, 21, 



24, 26, 27.] 

 Ogilvie Air-Speed Indicator. A speed instrument for aeroplanes. 



See Speedometer, Air-Speed Indicator. 

 O'Gonnan Tautness-Meter. See Tautness-Meter. [4, 6, 21.] 

 Ohmmeter. An instrument for the direct measurement of 



electrical resistance in ohms. 



Oil- Boiling Thermometer. See Thermometer. [5, 13, 16, 17, 21] 

 Oil-Fuel Thermometer. See Thermometer. [13, 15, 16, 17, 21, 



28] 

 Oil Hydrometer. A hydrometer (q.v.) for indicating the specific 



gravity of oil. [5, 13, 15, 16, 17, 21, 28] 

 Oil Rod. A dipping rod for measuring the contents of oil 



vessels. [6, 13, 15, 28] 

 Oil-Tempering Bath Thermometer. See Thermometer. [5, 6, 



13, 15, 16, 17] 



Oil-Tester, Thurston's Patent. An instrument for testing lubri- 

 cating oils. There is also a recording instrument, railroad 



and steamship pattern. [13, 15] 

 Oil Weight, Redwood Standard. A standard brass weight used 



in the measurement of the oil in tanks. [13, 15] 

 Oleine Tube. A graduated tube for determining oleine in oils 



and fats. 

 Oleometer. A hydrometer (q.v.) adapted for determining the 



relative densities of oils. [5, 13, 17, 21] 

 Oleorefractometer, Jean's. A refractometer (q.v.) for the analysis 



of butter, fats, oils, glycerine, turpentine, etc. The refractive 



I 



