45, CORNHILL, E.G., AND 122, EEGENT STEEET, W., LONDON. 



11 



FIG. 



FIG. 14. 



instrument is arranged in the most compact and convenient form 

 for safety in travelling, and obtaining very accurate altitude 



measurements. 



Price, Including Brass Tripod Stand (as fig. 12) and Travelling 

 Case for the Barometer, with English or Millimetre Scale 10 10 



12. Standard Mountain Barometer of simpler form and 

 smaller tube. Price 8 8 



13. Standard Syphon Barometer (Gay Lussac's), divided 

 on the glass tube, suited for Laboratory use (fig. 13), mounted on 

 mahogany board, with thermometer and two verniers. Price 550 



14. Standard Syphon Tube Mountain Barometer (Gay 

 Lussac's), with attached thermometer, and improvement in the 

 tube for excluding air. This is shown in fig. 14, and known as 

 Gay Lussao's Air Trap : its use being to arrest any air that may 

 pass up between the glass and the mercury. The bubbles of air 

 are stopped and collected at the shoulder of the trap at K, and 

 cannot possibly get up into the tube. This barometer is light and 

 convenient for travelling. The graduations are upon the brass 

 tube with verniers at each extremity reading from the centre. By 

 adding the two readings together the correct height of column is 

 obtained to -g^th f an inch. 



Price of Barometer, in leather travelling case, with Brass 



Tripod Stand (fig. 15) 880 



This Syphon Barometer does not require correction for either 

 capillarity or capacity, as each surface of the mercury is equally 

 depressed by capillary attraction, and the quantity of mercury 

 which falls from the long limb of the tube occupies the same length 

 in the short one. The barometric height must, however, be cor- 

 rected for temperature, as in the cistern barometer. 



15. Board of Trade Standard or Kew Marine Barometer, 

 bronzed brass frame, with iron cistern, and mounted on mahogany 

 board, as in fig. 16. The graduations on the scale are so arranged 

 that the exact reading can be obtained at once, without any previous 

 adjustment of the level of the mercury in the cistern, as in the Fortin 

 barometer. Price 550 



16. Meteorological Offi.ee Station Barometer, Bronzed 

 metal frame, with iron cistern and glass scales mounted on mahogany 

 board. Exact readings can be taken without any previous adjust- 

 ment of the mercury, fig. 17. Price, 770 



17. Board of Trade Marine Barometer, similar to 

 No. 16, but mounted on arm, with gymbal ring, instead of a 

 mahogany board. Price, Packed in travelling case .440 



