59 



Auxanometer Klinostat. A similar instrument to the above, but 

 arranged to take the plant in a vertical or horizontal posi- 

 tion, so as to determine the effect of gravity on the plant's 

 growth. 



Auxograph. An instrument for indicating the growth of a plant. 

 Averaging Instrument, Goodman's. An instiument for finding 



the averages in indicator diagrams. [15] 



Aviation Compass. See Compass. [9, 13, 15, 16, 17, 20, 21, 27.] 

 Aviation Revolution Indicator. See Revolution Indicator. [6, 



15, 17.] 

 Axonieter. An instrument to determine the required height of 



the bridge of a pair of spectacles. 



Ayrton-Mather Galvanometer. See Galvanometer. [4, 16, 19.] 

 Azimuth Compass. See Compass. [13, 15, 16, 17, 20, 21, 25, 27-. 



28.] 



Azimuth Dial. See Dial. [13, 15, 16, 17, 20, 21, 24, 27, 28.] 

 Azimuth Mirror. See Mirror. [13, 15, 16, 17, 28.] 

 Azotometer. An instrument for measuring or determining the 

 proportion of nitrogen in air or in a mixture of gases. 



Back Staff. An instrument formerly used at sea for taking the 

 sun's altitude, so called because the back of the observer 

 was turned towards the sun when he made the observation. 



Bacteriological Incubator. An apparatus, heated by gas, oil or 

 electricity, for promoting the growth of bacteria. [2, 3, 26.] 



Bacteriological Steriliser. A sterilising apparatus for bacterio- 

 logical work. 



Bacterioscope. An instrument for the microscopical examina- 

 tion of bacteria. [2.] 



Baines's Slide-Rule. See Slide-Rule. [15.] 



Bake-oven Thermometers. See Thermometer. 



Baker's Temperating Thermometer. See Thermometer. 



Balance. An instrument for determining equality or difference 

 of weight. [2, 4, 13, 17, 20] 



Balance, Actinic. See Bolometer. 



Balance, Aerodynamic. An instrument for the investigation of 

 the stability of aeroplanes by means of experiments on 

 models. The model aeroplane is suitably fixed to the 

 balance, which projects into a wind channel through which 

 a stream of air at the required velocity can be driven. 

 The forces acting on the model are counterbalanced by the 

 adjustment of weights on the arms of the instrument. 



Balance, Chemical. A sensitive balance consisting essentially of 

 a horizontal beam supported on a knife-edge, either of steel 

 or agate, on the top of a pillar. From the ends of the beam 

 pans are suspended, also from knife-edges. [2, 5, 17, 20] 



Balance, Electric. An instrument for measuring electric currents 

 by balancing electro-magnetic forces between conductors 

 against gravity. 



