412 REPORT— 1892. 



pressure, aud the length of time during which this pressure was maintained ; 

 (4) the rate at which the pressure was reduced, and the time occapied in 

 reducing the pressure ; (5) the number of times the several presses were 

 brought into operation, and the distribution of the work during the 

 different parts of the day. 



A very delicate pressure-gauge by Messrs. Richard Freres is described 

 in the report of Colonel Sebert previously mentioned,' which will 

 measure the variation of the water column by a fifth of a millimetre. 



Recording anemometers for recording the pressure of the wind also 

 belong to this type of instrument, and one may be mentioned, designed 

 by Mr. Osier, F.R.S., of Birmingham, an example of which is in opera- 

 tion in the Bidston Observatory, near Liverpool, also at Kew and Green, 

 wich. A disc exactly 2 square feet in section is presented to the wind, 

 and the pressure is transmitted to a small carrier, having the recording- 

 pencil attached, in the observatory below, and thus a record is given upon 

 a revolving drum. 



The last instruments coming under this class which maybe mentioned 

 are the 'stress and strain recorders,' which have now become a jaart of 

 the equipment of all engineering laboratories, in connection with machines 

 for testing the strength of materials, and it is becoming the practice, in 

 better classes of testing, to take and furnish an autogi-aphic record with 

 every specimen tested. The forms of these instruments are numerous, 

 an account of the principal types being given in Professor Unwin's book 

 on the testing of materials,^ and in a paper by Professor Kennedy..^ An 

 account of one designed by the writer of this report is given in the 

 'Minutes of Proc. Inst. C.E.,' vol. Ixxxviii. p. 101. 



c. Electrical instruments — voltmeters, ammeters or ampere meters. 

 Watt meters, and galvanometers — are all made of the first recording- 

 type, and are described in the report of Colonel Sebert, already alluded 

 to, as being manufactured by Messrs. Richard Freres. An example of an 

 ampere meter record has already been given. They are also described 

 and illustrated in the catalogue of the makers, in which the record from 

 these instruments gives everything which is to be known about an 

 electric station continuously, including the times of starting, maximum 

 and minimum production of the electric current, and the way in which 

 the machines have worked. 



d. Instruments for recording velocity may be divided into two 

 classes : (1) Those which actually record the velocity by the height of 

 the ordinate on a revolving drum ; and (2) those which indirectly do so 

 by the distance travelled over the surface by the pencil in a given period 

 of revolution. 



The most common method in which the former acts is by some kind 

 of governor, operated by means of the steam-engine, which raises or 

 depresses the pencil according to the position of the governor balls. 



An instrument of this kind, which is now well known, is the ' Mos- 

 crop ' recorder,* and similar instruments have been designed by Messrs. 

 Bailey and Mr. Edson. The application of these instruments has been 



' Lc Rapport de M. le Colonel Srhcrt a la Societe d' Encouragement pour I'lndus- 

 trie Naiionale, November 1883, p. 102. 



- Testing of Materials of Construction, by Professor Unwin. Macmillan & Co. 



^ ' Equipment of Engineering Laboratories,' by Professor A. B. W. Kennedy. 

 Min. Proc. C.E., vol. Ixxxviii. p. 1. 



■* Minutes of the Proceedings of the Institute of Mechanical Engineers, 1884, p. 150. 



