26 



to the temperature indicated by the attached thermometer of the 

 apparatus. 



65. Howso7i!s 'barometer. — This ingenious and novel device is shown 

 in section in Figure 20. The barometer tube is large in diameter and 

 longer than usual. The cistern is recurved and extends as a long core 

 up inside the barometer tube, reaching within 3 or 4 inches of the top 

 01 the column of mercury. The proportions are arranged to be such 

 that the upward pressure of the air on the under side of the cistern is 

 sufficient to sustain the cistern and contents suspended from the end 

 of the barometer tube. 



riGURE 18. — Dial 

 barometer 



FiGUsa 19. — Sympiesometep 



When a change of pressure occurs the cistern is caused either to 

 ascend upon a barometer tube or to move down to a new position of 

 equilibrium, and, by selecting suitable proportions between the inter- 

 nal diameter of the barometer tube and the thickness of its walls in 

 relation to the diameters of the core and cistern, the movement of the 

 latter up and down the tube with changes of atmospheric pressure 

 can be made to represent pressures upon a greatly magnified scale. 



66. Magnifying siphon harometer. — Figure 21 illustrates still an- 

 other expedient by which the indications of a plain mercurial barom- 

 eter may be greatly magnified. The short leg of a siphon barometer 

 is extended upward, in the manner shown. The small-bore tube a is 

 enlarged at the top to have the same diameter as the cistern portion. 



