132 



Orthoscope. An instrument designed to show the condition of 



the superficial portion of the eye. 

 Orthoscopic Eyepiece. An eyepiece giving a specially large field 



of view ; a Kellner eyepiece. Apparent field of view, 40. 



[l, 2, 3, 10, 20, 21, 22, 23, 25, 26, 27.] 

 Orthoscopic Lens. An arrangement of two achromatic compound 



lenses separated by an interval. [1, 21, 23, 26, 27.] 

 Oscillating Prism Telescope. See Telescope. 

 Oscillating Table, Bryan's. An instrument for demonstrating 



the properties of moments of inertia. [19.] 

 Oscillograms. Diagrams produced by means of the oscillograph 



(q.v.). [4.] 

 Oscillograph. An instrument for recording the wave form of 



current and voltage in alternating current circuits. [4.] 

 Oscillograph, Duddell. An oscillograph which traces out and 



records photographically to uniform scales curves connecting 



current or voltage with time. [4.] 

 Oscilometer. An instrument for measuring the angle through 



which a ship rolls at sea. [5, 13, 15, 17.] 

 Osmometer. An instrument for measuring osmosis in different 



liquids. 

 Osteophone. An instrument for the transmission of auditory 



vibration through the bones of the head, so as to be appre- 

 ciated as sounds by persons deaf from causes other than 



those affecting the nervous apparatus of hearing. 

 Ostwald's Capillary Electrometer. See Electrometer. 

 Ostwald's Water Thermostat. See Thermostat. 

 Otacoustic. An instrument to facilitate or improve the sense 



of hearing ; an ear-trumpet. 

 Otheoscope. An instrument for exhibiting the repulsive action 



produced by light or heat in an exhausted vessel. 

 Othoscope. An instrument for holding water round the eye to 



enable the interior to be seen. 



Otoscope. An instrument for viewing the interior of the ear. 

 Outside Callipers. See Callipers. [17, 20, 21, 25.] 

 Oxide Testing Thermometer. See Thermometer. [13, 15, 21.] 

 Ozometer. See Ozpnometer. 

 Ozonometer. An instrument for ascertaining the amount of 



ozone in the atmosphere. [6, 17, 21.] 

 Ozonoscope. An apparatus employed to indicate the presence 



or amount of ozone. 



Paceometer. See Passometer. [2, 15, 21, 24, 27.] 



Pachometer. An instrument for measuring thickness, as of the 



glass of a mirror, or of paper ; a pachymeter. [2.] 

 Pachymeter. See Pachometer. [2.] 

 Paget Angle Sextant. See Sextant. [16, 27.] 

 Paget Artificial Horizon. See Artificial Horizon. [16.] 

 Paget Compass Card. A compass card (q.v.) with short needles. 

 [15.] 



