410 REPOET 1892. 



' The determination of the divisions on the diagram, and of the 

 angular displacements of the ball, corresponding to certain velocities, 

 were the results of numerous and careful experiments carried out on the 

 old Bolton and Manchester Canal by the makers of the instrument, and 

 Mr. Hurtzig was satisfied that the instrument would give all the informa- 

 tion required ; and since the date it was erected it has worked well, and is 

 now in perfect order.' 



For waterworks such recorders are approximate water-meters, 

 every increase in the height of the water measuring a known quantity 

 (say 1,000,000 gallons for every eighth of an inch rise), so that they 

 form a check upon the water-meters supplying the town. 



The late L. J. Crossley, Esq., designed a rainfall-recorder which, 

 though arranged for ordinary purposes, could, during a thunderstorm or 

 sudden downfall, be so altered as to cause the drum to revolve once in 

 an hour instead of once in twenty-four hours by means of a wheel put 

 in gear by a magnet worked from Mr. Crossley's house, more than a mile 

 distant. The matter of distance presents no difficulty in the way of 

 obtaining a continuous record of the height of water in a reservoir or 

 aqueduct ; thus, Messrs. Richard Freres make an instrument, designed by 

 M. Grivola, in which only one wire is employed, which may be used to 

 record the level by electric means at any distance. 



For short distances, such as about 50 yards, the same makers have 

 an instrument which consists of an iron case, perforated with holes, con- 

 taining an indiarubber bag filled with air. This bag is connected by 

 means of a copper tube to a self-recording pressure-gauge, and the case 

 is immersed in the liquid. The air pressui'e, and consequently the height 

 of the liquid, is indicated and recorded by the pressure-gauge, and as 

 there exists no contact between the liquid and the air, the latter cannot 

 get dissolved and the indications are always correct. 



The tide-gauge, designed by Sir William Thomson, is well known, and 

 has the peculiar feature of an inclined path for the slider, which holds the 

 recording pencil, necessitating a correspondingly inclined position for the 

 axis of the barrel on which the paper is wound.' 



A more elaborate tide-gauge has been designed by M. Lechatelier, and 

 made by Messrs. Richard Freres.- This is used to record the height of 

 the water in the basin of La Villette. 



h. Instruments for recording the pressure of steam, air, or water 

 form probably the most important of all classes of such self-recording 

 apparatus. 



First in importance must rank the steam-engine indicator. 



The use of this instrument, since the time of its invention by James 

 Watt, has continually increased, and so great has been the attention given 

 to its improvement that a treatise of considerable size might be written 

 on this subject alone. In essential features the instrument remains the 

 same as it was one hundred years ago, consisting, as in almost every re- 

 cording instrument, of two parts — of a moving pencil and moving paper, 

 whose paths are respectively at right angles to each other. But the intro- 

 duction of higher pressures and quicker speeds has necessitated numerous 

 but important changes of detail ; hence some kind of parallel motion is 



' The 'Tide-gauge, Tidal Harmonic Analyser, and Tide-predicter,' by Sir Wm. 

 Thomson. Mm. Prop. Inst. C.JS., vol. Iv. p. 2. 

 - Atumles dcs Fonts ct Chaussres, Mai 1885. 



