VI. VELOCITY. 103 



44a. Mercurial Indicator and Counter. 



T. R. Harding and Son. 



The above instrument is a combination of Harding's integrating counter 

 and Brown's patent indicator, for which T. R. Harding and Son are sole 

 licensees in Great Britain. 



The mercurial indicator shows the speed per minute of the shaft above 

 it ; the counter records AaZ/'the number of revolutions of the same shaft. 



The principle of the mercurial indicator is very simple. The tubular arms 

 of the rotating U tube are connected with the central glass tube, and when 

 the instrument is at rest the mercury settles to a level in the glass tube and 

 arrives at the zero of the scale. When the instrument is rotated, the mercury, 

 owing to the centrifugal tendency, rises in the arms and sinks ill the central 

 tube to a greater or less extent according to the speed. 



These indicators are of great importance for marine, stationary, and loco- 

 motive engines, as well as for various kinds of machinery. 



By means of the counter and a watch, the accuracy of the mercurial 

 indicator can at any time be verified. 



47. *' The Motometer," a machine to indicate the number 

 of revolutions made per minute, or other portion ,of time, by a 

 steam engine or revolving shaft, or any body having intermittent 

 motion, so that by simple inspection of a dial the rate of speed may 

 be seen. ff. Faija. 



This instrument is constructed so as to indicate by a positive motion direct 

 from the engine or other moving body to which it is attached, and is of 

 purely mechanical construction independent of all centrifugal and other 

 forces of an indirect nature. The indication is consequently absolute and not 

 comparative. 



The instrument is made in various forms to suit differences of speed, from 

 the slow stroke of a pumping engine to the high speed of a locomotive, &c. 



The skeleton machine exhibited is suitable to indicate the ordinary speed 

 of a marine or stationary engine, while the one attached to the shafting is 

 adapted for very high speeds. 



395. Hearson's Patent Strophometer or Revolution 



Indicator, an instrument for showing at a glance, by the position 

 of a pointer on a graduated dial, the number of revolutions per 

 minute an engine is at the time making. Elliott Brothers. 



395a. Working Model of Revolution Indicator, for 



engines and machinery, by J. Wimshurst. J. F. Planner*/. 



415. Mercurial Gyrometer, or " orbit meter." 



Royal Polytechnic Academy {Prof. Reuleaux, Director}, 

 Berlin. 



The instrument indicates directly the angular velocity of an axle, shaft, 

 &c., in figures showing the rotations per minute. The reading takes place 

 on an alcohol column, which shows on one side a millimeter scale, and on 

 the other the rotation numbers. The instrument is so arranged that the 

 scale of the rotations has uniform graduation. 



532b. Reuleaux's Ball-Gyrometer. 



H. ffddicke, Engineer, Demmin, Pomerania. 



The object of the instrument is to indicate the rotations made per minute 

 by any rotating body brought into connexion with the same. The number 



