of a silver salt. The anode consists of a plate or rod of pure 

 silver and the cathode of a platinum bowl. [4.] 



Voltmeter. Any instrument for measuring the pressure, electro- 

 motive force, or difference of potentials at the ends of an 

 electric current. [10, 16, 21.] 



Voltmeter, Electrostatic. A voltmeter for the measurement of 

 the potential difference between two points, by means of 

 the electrostatic forces between moving and fixed elements, 

 but no current flows through the instrument itself. 



Voltmeter, Recording. A voltmeter giving a continuous and 

 visible record on a chart of variations of potential. 



Volumescope. An instrument, consisting essentially of a glass 

 tube, provided with a graduated scale for exhibiting to the 

 eye changes of volume of a gas resulting from chemical 

 action or the like. 



Voluminometer. An instrument for measuring the volume of a 

 body, especially a solid, by means of the difference in tension 

 caused by its presence and absence in a confined portion 

 of air. 



Vulcaniser Thermometer. See Thermometer. [5, 13, 15, 17.] 



Wallis's Barometer Adjunct. A small reading microscope (q.v.). 



[6, 13.] 



Walpole's Colorimeter. See Colorimeter. 

 Warm Stage. A contrivance for keeping a specimen at an even 



temperature when examining under a microscope. [2, 3, 



22, 26.] 

 Watchmaker's Eyeglass. A magnifying lens mounted for fixing 



in one eye. [2, 3, 15, 17, 20, 21, 22, 26.] 

 Water-Analysis Apparatus. Any apparatus for the analysis of 



water. 



Water-Barometer. See Barometer. [13, 17.] 

 Water Finder, Redwood. An instrument for determining the 



amount of water at the bottom of an oil tank. [13, 15, 16.] 

 Water-Gauge Glasses. Glass tubes fitted to boilers, etc., to 



indicate water level. [5, 15, 17.] 

 Water Hammer. A vessel partly filled with water, exhausted of 



air, and hermetically sealed ; when reversed or shaken, the 



water, being unimpeded by air, strikes the sides in solid mass 



with the sound like that of a hammer. [17, 21.] 

 Water-Testing Apparatus. For testing the hardness of water. 

 Water Thermometer. See Thermometer. 

 Watkin Clinometer. See Clinometer. [13, 15, 21, 25, 26, 27.] 

 Watkin's Heat-Recorder. Consists of a small block of refractory 



material, having circular recesses sunk into top face, into 



which are placed fusible pellets of definite composition and 



melting point. See also Seger Cones. 

 Wattmeter. An instrument for directly measuring, in watts, 



the work- rate, or electrical power, of an electric current in. 



a circuit. It is usually a form of electro-dynamometer (q.v.). 



