130 



power of the oil or fat under examination is compared with 

 the refractive power of a standard oil. [13, 26.] 



Ombrometer. An apparatus or instrument to measure the depth 

 of rain which falls ; a rain-gauge (q.v.). [17.] 



Omnigraph. See Pantograph. [21.] 



Omnimeter. A theodolite (q.v.) with an additional scale for 

 measuring distances. [2, 13, 15, 21, 25, 26, 27.] 



Oncograph. An instrument for recording the measurements 

 made by the oncometer (q.v.). 



Oncometer. An instrument for measuring the variations in 

 size of the internal organs of the body, as kidney, spleen, etc. 



One Handed Dividers. Improved chart dividers ; can be opened 

 and shut with one hand. See Divider. [5, 6, 13, 15, 16, 17, 

 21, 28.] 



One-Tenth of a Second Time-Marker. In mine explosions 

 apparatus (q.v.) used in connection with the recording 

 manometers to determine time-intervals. [4.] 



Opacities Apparatus. Designed by Prof. T. B. Wood, Professor 

 of Agriculture, University of Cambridge, more particularly 

 for ascertaining and comparing the baking quality of 

 wheat. Can be used for comparison of the opacity of 

 liquids. [19] 



Opaque Disc Revolver. An apparatus for holding and rotating 

 a microscopic object so that five sides of a cube can be 

 examined without removal from the microscope. [2, 3, 26.] 



Opeidoscope. An instrument consisting of a tube, open at one 

 end, covered with a flexible membrane at the other, which 

 carries a small mirror for exhibiting on the screen vibrating 

 motion caused by sound. [4.] 



Opera-Glass. A small Galilean binocular telescope (q.v.). It 

 has a concave eyeglass and a convex object-glass, so that 

 the image is not inverted and little light is lost. [2, 5, 9, 

 10, 13, 15, 16, 17, 20, 21, 24, 26, 27, 28.] 



Operameter. An attachment to a machine to indicate the 

 number of rotations of a shaft. [5, 6, 13, 15, 17.] 



Ophthalmic Mirrors. A special form of mirror used for the 

 examination of the eye. [2, 3, 10, 20, 21, 26] 



Ophthalmic Spinthariscope. An instrument to test the sensitive- 

 ness of the retina of the eye by reference to a standard light 

 emitted by radium. [3, 26] 



Ophthalmoscope. An instrument for viewing the interior of 

 the eye, particularly the retina. Light is thrown into the 

 eye by a mirror, usually concave, and the interior is then 

 examined with or without the aid of a lens. [2, 3, 17, 20, 

 21, 26.] 



Opisometer. An instrument with a revolving wheel for measuring 

 a curved line on a map. [2, 15, 17, 20, 21, 24, 25, 26, 27, 28.] 



Opsiometer. An instrument for measuring the limits of distinct 

 vision in different individuals, for determining the focal 



