VII. RECORDING INSTRUMENTS. 711 



anil t-.'ierahlv well handled, the instrument will, practically, ne*ver refuse to 

 work. 



(5.) The registering of the temperature of the instrument might prove 

 useful in other observations, since it gives the temperature of a closed space. 



(6.) Not the least of the advantages is the cheapness of the instrument. 



The theory of this apparatus is given in full in Volume XI. of Carl's 

 " Repertoriurn fur Experimentalphysik." 



G. Lorenz, Chemnitz (Lachseri), has undertaken the construction of the 

 apparatus. 



2891. Kreils' Barograph, formerly in use at the Kew Obser- 

 vatory, for registering the movement of the barometer. 



Kew Committee of the Royal Society. 



An instrument employed at the Kew Observatory in 1845, for the purpose 

 of registering automatically the height of the barometer. It consists of a 

 syphon barometer, having a float resting upon the surface of the mercury, in 

 the open end of the tube. Immediately above the tube a lever is fixed 

 horizontally, and a cord, wrapped round a sector on the short arm, passes 

 down and is attached to the float. The other end of the lever carries an 

 ordinary pencil, which, being struck every five minutes by a hammer moved 

 by a clock, makes a dot upon a sheet of paper fixed to a frame drawn in front 

 of it by clockwork. 



2892. Ronalds' Photo-Barometrograph, for registering 

 photographically the changes in the height of the barometer, for- 

 merly erected at the Kew Observatory. 



Kew Committee of the Royal Society. 



An instrument for registering the variation in the height of the barometer 

 upon a daguerreotype plate; constructed in 1847 by Mr. Francis Ronalds, 

 afterwards erected at the Kew Observatory, and described by him in the 

 British Association Report for 1851. 



The light from an argand lamp, after passing through a condensing lens, 

 falls on a narrow slit cut in a metal plate attached. A barometer tube, the 

 mercury in which, by rising or falling, varies the length of the slit illuminated. 



An achromatic combination of lenses, by Voigtlander, throws a magnified 

 image of the bright slit upon an aperture in the case, past which a daguerreo- 

 type plate is moved slowly by clockwork, and so registers the changes in 

 the height of the barometer. 



The barometer itself, together with its cistern, which is of large area, is 

 suspended from an arrangement of levers and zinc rods, on the principle 

 of the gridiron pendulum, in such a manner as to render the indications 

 unaffected by fluctuations of temperature. 



An improved form of this instrument, in which the photographic image is 

 impressed upon paper, is now in use at Kew, and at many other observatories. 



2892aa. Photographic Barograph, as employed at the 

 observatories in connection with the Meteorological Office. 



Meteorological Committee of the Royal Society. 



This instrument is described in the Report of the Meteorological Committee 

 of the Royal Society for 1867. It is the improved form of Ronald's baro- 

 graph, No. 2892. 



2892a, Baroxnetrograph. M. Breguet, Paris. 



