L. CASELLA'S CATALOGUE 



FIG. 17. 



16. Mountain Barometer, Gay Lussac's syphon 



tube, with vernier to each limb, reading to 

 '002 of an inch, the difference between the 

 two readings giving the height of the baro- 

 meter. In improved leather-covered shield 

 case . . . 660 



(If with tripod starfd, similar to that for No. 15, 8.) 



17. SELF-KEGISTEEING ANEEOID BAEOMETEE. In 



this elegant arrangement a vertical cylinder 

 is caused to revolve by means of clockwork > 

 and the barometric variations accurately 

 marked at every hour on ruled metallic paper 

 by the action of a large and strongly made 

 Aneroid Barometer, the paper being changed 

 once a week. By connecting the lines (as in 

 No. 18) an accurate barometric diagram, show- 

 ing dates and times of changes is obtained, 

 whilst the clock and aneroid respectively, form 

 excellent instruments for showing exact time 

 as well as constant changes in the weather 

 (fig- 17) . 22 



18. Self-Registering Mercurial Barometer, or Barograph, for recording the baro- 



metric variation on ruled metallic paper. In this arrangement a vertical 

 cylinder of about 4 inches diameter, is made to revolve once every seven 

 days, by means of clock-work. A metallic pencil rising and falling with the 

 mercury marks this paper at every hour, the paper being changed once a week. 

 The date, time, etc., of every change of pressure is thus correctly indicated, and 

 being connected by lines drawn from point to point gives a correct con- 

 tinuous diagram of whatever changes may have occurred. The mercurial 

 column and timepiece are also observable at any moment, the instrument 

 thus forming an ordinary barometer as well as an excellent eight-day 

 clock (fig. 18). The size being about 13 inch, wide X 8 inch, deep X 36 

 inch, high . . . . - . . . 18 10 



19. Ring's Barograph, or Self-registering Barometer, as erected in the Liverpool 



Observatory. In this construction the barometric column may be caused to 

 range from five to ten inches for each inch in the ordinary barometer, and to 

 record continuously the smallest as well as the largest fluctuations which may 

 occur in the pressure of the atmosphere. . . . 25 



18. 



