rectangular rings of aluminium suspended in a magnetic 

 field. Induced currents which follow exactly the variations 

 of the current or E.M.F. under investigation are produced 

 in these rings, which are therefore deflected. The deflections 

 are observed by reflection from a mirror on to a screen. [4.] 



Rheometer. An instrument for measuring the force of an 

 electric current. [4.] 



Rheomotor. Any apparatus which originates an electric current. 



w 



Rheoscope. An instrument for detecting an electric current. [4.] 

 Rheostat. An instrument consisting of an adjustable resistance 



for the gradual and continuous regulation of the strength 



of current in an electric circuit. [16, 19, 20, 26.] 

 Rheotome. An instrument which periodically interrupts an 



electric current. [4.] 

 Rheotrope. An instrument which periodically inverts an electric 



current. [4.] 

 Rhinoscope. A small instrument for use in examining the 



posterior nares, the rear portion of the nostrils. 

 Rhomb (Fresnel's). A rhomb or oblique parallelepiped of 



crown glass so cut that a ray of light entering one of its faces 

 %$ at right angles shall emerge at right angles at the opposite 



face, after undergoing within the rhomb at the other faces 

 J$jl " two reflections ; used for experiments with polarised light. 



See also Prism, Pentagonal. [3, 14, 26.] 

 R.H.S. Calculator. A tubular form of slide-rule (q.v.) designed 



by Prof. R. H. Smith, having a scale line of 50 inches. [15.] 

 Rhumboscope, Mooney's. A special form of station pointer for 



coastal navigation and chart work. [15.] 

 Rhysimeter. An instrument for measuring the velocity of fluids 



or the speed of ships. [13.] 



Rhythmometer. Any instrument for marking time to move- 

 ments in music. 

 Richard's Indicator. An early form of engine indicator (q.v.). 



[5, 13, 15, 16, 17, 21, 28.] 



Richmond's Slide-Scale. For the estimation of fat in milk. [26] 

 Right- Angle Thermometer. See Thermometer. [5, 13, 15, 17, 



21.] 

 Ripograph. An instrument for determining the efficiency in 



flight of an aeroplane. Altitude, velocity, longitudinal 

 p^ inclination, time, engine speed, positions of control levers, 

 ~* and rolling movement are indicated. [4.] 

 Ritchie's Photometer. See Photometer. 

 Road-Pen. A twin drawing-pen for the insertion of roads on 



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

 Road Tracer. A sighted balance level for taking road gradients. 



[6, 13, 15, 17, 21, 27.] 

 Robart's Machine-Gun Protractor. A transparent gunnery 



instrument for range-finding work. 

 Robinson Anemometer. See Anemometer. 



