80 



NEGUETTI AND ZAMBBA, HOLBOKN VIADUCT, E.C., 



FIG. 30. 



36. Recording Mercurial Barometer or Barograph for automatically 

 recording the variations of atmospheric pressure by Photography. Recom- 

 mended by the Meteorological Committee of the Royal Society, and used by 

 many of the principal Meteorological Observatories. 



Fig. 30. exhibits the general arrangement of this Barograph. B is a 

 Standard Mercurial Barometer mounted upon a mahogany board and table, 

 lacing it is a Drum D, to which is attached the sensitised Photographic Paper. 

 This cylinder is revolved once in 24 or 48 hours by the clock C. A Condensing 

 Lens, E, projects the light from the Gas Burner G through the space F over the 

 edge of the mercurial column, and thence to the photographic combination lens P, 

 by which an image of the mercurial column is formed upon the sensitive paper 

 on the drum for a regulated space of time. A screen or shutter L acted 

 upon by the clock cuts off this image for the space of four minutes every two 

 hours, leaving white lines upon the photographic paper representing intervals 

 of two hours. At the side of the barometer tube are placed two zinc rods 

 attached to the barometer board at the lower ends at A. These rods are con- 

 nected at their upper ends with a delicate mechanical arrangement H and K, 

 so contrived as to compensate for varying Thermometric changes in the 

 mercurial column, these variations of temperature being also recorded upon 

 the sensitive paper. 



Attached to the apparatus is, a glass cylinder, M, (of the same internal 

 diameter as the Barometer tube), partly filled with mercury, into which is placed 

 a sensitive Standard Thermometer for giving the temperature of the surround- 

 ing air. B is an adjusting screw for regulating the height of the barometer 

 upon its support. The apparatus when in action is enclosed in a light tight box. 



The Barograph is constructed to special older, the cost varying from 

 Sixty to Seventy Guineas. 



