408 



EEPOET — 1892. 



prevent errors of r.cale, to have them lithographed with ruled lines. Such 

 paper should always be tested, and, if possible, the actual scale marked 

 on it. 



2. Coming now to the means of moving the paper or other prepared 

 surface, it may be said that the almost universal practice is to adopt the 

 cylindrical drum for carrying the record. Moreover, it may be said 

 that in the majority of cases this drum is turned by clockwork, although 

 there is one most important class of instruments in which this is not the 

 case, namely, the steam-engine indicator. 



For large instruments — such as tide-gauges, anemometers in observa- 

 tories — a pendulum or weights are used for giving motion to the barrel, 

 but in the majority of cases this conti-ivance would occupy too much 

 space, and springs are employed. Continuous papers are frequently used, 

 enabling records to extend over long periods of time, as with the Edson 

 steam-pressure recorder ; but the general practice is to have a special 

 chart for each day. 



The manner of connecting this chart to the barrel is a matter of no 

 little importance. In the case of the steam-engine indicator the barrel 

 does not turn through a whole revolution, and hence the projecting clips 

 do not present a serious objection ; but in barrels which revolve this 

 matter must be provided for, and special precautions are taken by 

 Messrs. Richard, Bailey, and others to prevent injury to the recording- 

 point. 



There are some recorders in which a flat surface is used, such as 

 Bristol's recording pressure-gauge, on which a circular sheet of paper is 

 attached to a revolving dial, and the pressures are recorded radially, or 

 nearly so, while time is measured round the circumference. 



A special feature of Messrs. Richard Freres' recording instruments is 

 to be found in the fact that the recording-point is almost invariably 

 carried on a lever working about a centre, and hence the paper on their 



Fig. 35. 



instruments on which the record is obtained has to be ruled in a special 

 manner, an example of which, taken from one of their self-recording 

 ampere meters, is given in tig. 35. A report on the subject of Messrs^ 

 Richard's instruments has been given by M. le Colonel Sebert.' 



' 'Notice sur les Instruments Enregistreurs construits par Richard Freres, 

 comprenant le Eapport de M. le Colonel Sebert 'd, la Societe d'Encouragement pour 

 Industrie nationale et I'Expose des Perfectionnements et Applications Nouvelles.' 



i 



