70 Mr. R. T. Glazebrook on the Value of 



it was suggested by Mr. Swinburne that the most useful 

 function of such an indicator would be to continually show 

 the diagram on a screen in an engine-room, so that at every 

 instant the engineer would not only know the pressure of 

 steam in his boiler, but also the pressure at every instant in 

 the cylinder. 



I quite forgot to put this in my paper, although its im- 

 portance was not unknown to me. I am now attaching an 

 indicator to each end of the cylinder of my driving-engine 

 at Finsbury. These will receive their miniature piston-motion 

 from one rod. One gas-jet will throw from the two mirrors 

 two diagrams upon a screen some seven feet away from the 

 mirrors, and these diagrams will be visible from nearly every 

 part of the engine-room at all times. In the room at present 

 there are not only very visible pressure- and vacuum-gauges 

 and a speed-indicator (not a counter), but also a dynamo- 

 meter coupling, which shows at a glance the actual horse- 

 power which is being transmitted along a shaft. If, instead 

 of tracing the diagram with a pencil, I were to trace it with 

 the point of a planimeter, the reading might represent the 

 horse-power. 



It is unnecessary to describe here how the indicator might 

 be fixed to the valve-chest or receivers, or to other parts of 

 an engine, such as the air- and force-pumps ; or to pumping- 

 machinery generally ; or to engines driven by fluids. In 

 fact it may be said that I have made the discovery that the 

 beautiful method of observation of vibration of M. Lissajous 

 has hitherto been neglected in its applicability to all sorts of 

 practical purposes. Quite a number of other applications of 

 the reflected beam of light principle suggest themselves. 



XI. On the Value of some Mercury Resistance Standards. 

 By R. T. Glazebrook, M.A., F.E.S., Fellow of Trinity 

 College, Cambridge *. 



IN a paper read before the Physical Society * on May 23, 

 1885, I described the results of a comparison between 

 the original standards of the British Association and some 

 copies of the mercury unit representing Legal Ohms made 

 by M. Benoit in Paris and sent to me by him. Two of these 

 copies have remained in my possession since that time ; the 

 third, at M. Benoit's request, was handed to Mr. Preece. 



* Communicated by the Physical Society : read May 9, 1891. 

 t Glazebrook, Phil Mag. October 1885 ; Proc. Physical Society, 

 vol. vii. 



