124 THE WORLD. 







hollow air-tight body a b c d is floating, having a tube, ef, opening 

 into the interior. When placed into the water it is evident that 

 a certain portion of the liquid will rise in the tube, and if light 

 weights are added either below or above, the whole body may be 

 caused to sink until its top is even with the surface of the fluid ; 

 ag is likewise a tube, which containing air, will prevent the in- 

 strument in great changes of weather from sinking to the bottom, 

 b h, is a wire, and g h and i b are threads stretched obliquely from 

 the tube to the wise. As the instrument rises and falls, a little 

 bubble of air on the thread shows the motion; the threads are so 

 located that when the bubble reaches i on the lower, it commences 

 at h on the upper one. A change of the pressure of the atmos- 

 phere preceding a wind or rain, by reason of a diminished press- 

 ure upon the surface of the water in the vessel, A B C D, forces 

 less of the fluid into the tube ef, and thus the specific gravity of 

 the included air being lessened by its expansion, the instrument 

 rises, and the bubble descends, corresponding with the fall of the 

 mercury in the barometer. When, on the approach of fine weath- 

 er, the atmosphere becomes calm, and of its usual density and 

 elevation, the water being forced into the tube cf, by the increased 

 pressure causes the baroscope to sink, and consequently the bub- 

 ble to rise. It is said that this instrument will show alterations in 

 the air 1200 times more accurately than the common barometer. 

 The inventor, Mr. Caswell of Oxford, observes that the bubble 

 is seldom known to stand still even for a minute ; that a small 

 blast of wind that cannot be heard in a chamber will sensibly 

 make it sink, and that a cloud passing over it always makes it de- 

 scend. The greatest objection to this very simple instrument is, 

 it is liable to be affected by the expansion of the included air by 

 heat. 



