90 On a New Form of Ergometer. 



nected to the spring of the instrument, so that any extension 

 of the spring moves E towards A, and consequently lengthens 

 the stroke of the pump. Now, when no energy is being trans- 

 mitted the spring of the ergometer is not extended and E has 

 a definite position between C and B ; and then the water dis- 

 charged by the pump is proportional to the number of revolu- 

 tions of the shaft ; but as soon as energy is transmitted the 

 spring is extended, and the discharge of water is increased by 

 the stroke being thus lengthened : the discharge then becomes 

 a measure of the work done in driving any given machine. 

 Instead of a small pump, a ratchet arrangement was tried ; 

 but the results were somewhat inferior to those with the pump. 

 The constants of the ergometer are found in the same manner 

 as when a disk integrator is used. 



The Speed-Indicator (second form, by the Author). 



This is based on the principle involved in the velocimeter 

 of Ramsbottom. In this instrument oil in a glass cylinder is 

 caused to rotate, the depression caused by rotation being a 

 measure of the number of revolutions. As this instrument 

 does not admit of sufficiently close reading for the ergometer, 

 the author uses mercury instead of oil ; this is whirled in a 

 cup with inverted edges. Into the centre of the mercury a 

 fixed tube dips, the end of the tube in the mercury being of 

 twenty times the capacity of the rest of the tube ; the tube is 

 partly filled with a tinted liquid ; the column of liquid is sup- 

 ported by the mercury. Now, when the mercury is whirled 

 the centre, in sinking, alters the capacity of the large end of 

 the tube ; and therefore the indications of the liquid in the 

 small end of the tube are very large for any change in the 

 depression of the mercury. The cup is caused to rotate by 

 means of any two of a set of change-wheels, these wheels 

 being used either to reduce or augment the speed of rotation 

 of the cup as the case may require. 



The speed-indicator is attached to the shaft driven by the 

 engine, and not always to the ergometer itself, because in 

 dealing with small amounts of work it is well that the work 

 done in moving the speed-indicator should not be added to the 

 work under test. 



The central shaft was made of compressed steel, by Sir J. 

 Whitworth Co. 



Taunton, December 19, 1882. 



