ON GEAPHIC METHODiS IN IJIECIIANICAL SCIENCE. 411 



ased to magnify the movement of the pencil and enable a small motion of 

 the piston-indicator to suffice, thus avoiding irregularities which would 

 otherwise occur at high speeds in the indicator diagram. 



The modified indicator which marked the chief change in the type of 

 the instrument was introduced many years ago to this country from 

 America by Messrs. Elliott Bros., of the Strand, London, and is known 

 universally as ' The Richards Indicator.' The details of other types are 

 given in various journals, mentioned under the title of ' Indicator ' in the 

 list appended to this report. The following are the principal makers, most 

 of whom have modifications of their own : Lloyd, Stanley, Darke, Negretti 

 <fc Zambra, Tabor, Orossley, Maginnis, Schaffer & Budenberg, as well as 

 many others. 



Recording steam-pressure gauges are employed for giving, as it were, 

 a history of the pressure in the boiler continuously. 



That made by Messrs. Bell consists of an eight-day clock actuating a 

 drum which revolves once every twenty-four hoars, the pencil being 

 moved by a treble tube Bourdon steam-gauge. 



Instruments very similar in design are made by the same firm for the 

 following purposes : Recording vacuum and hydraulic pressure, and for 

 use in waterworks in connection with pumping engines ; for chemical 

 works, to record the dates of absorbing and concentrating columns ; and 

 for steelworks and blast furnaces, for recording the blast pressures. 

 They are sometimes made with continuous paper, but this design is not 

 in particular favour, although it is a feature of the Bdson steam-pressure 

 recorder. In fact, there are between 2,000 and 3,000 of these instruments 

 in use, representing no less than thirty different varieties of design. 



Messrs. Richard Freres also make a steam-pressure recorder of this 

 kind, and there are several other designs, amongst which may be men- 

 tioned the Edson steam-gauge recorder, largely used in America. 



This instrument, unlike the other two previously described, which 

 were both constructed on the principle of the Bourdon gauge, has a 

 corrugated flexible surface, on which the pressure of the steam acts. 



Messrs. Schaffer & Budenberg have made for several years a record- 

 ing pressure-gauge, although no account of it has apparently appeared 

 in any paper. 



Recording aneroid barometers have been in recent years introduced 

 in very large quantities, and every French war- vessel carries such an 

 instrument, records of which are obliged to be always posted with the 

 ordinary log. 



The pressure of air in connection with collieries is of very great 

 importance, particularly in connection with the ventilating appliances ; 

 and Mr. Joseph Dixon, H.M. In.spector of Mines, feeling strongly on the 

 subject, has been instrumental in getting designed, by Messrs. Bailey, most 

 ingenious mine-ventilating recorders, notice of which appeared in the 

 ' Colliery Guardian.' ^ 



Messrs. SchafJ'er & Budenberg make a hydraulic press recorder which 

 gives several kinds of diagrams simultaneously of the work performed by 

 a system of hydraulic presses during either twelve or twenty-four hours. 

 The diagrams show : (1) The times when the several presses were brought 

 into action ; (2) the rate of increase of pressure, and the time occupied in 

 attaining the maximum, pressure ; (3) the amount of the maximum 



' GMerij Gmrdian, September 30, 1881. 



