on the Marine Barometer. <265 
tance to the commander of a ship, in warning him of the 
approach and termination of bad weather, and of changes in 
the direction of the wind, even in the present state of meteo- 
rological knowledge, that no officer in a long voyage should 
be without one. Some experience is required to understand 
its language, and it will always be necessary to compare the 
state of the mercury with the appearance of the weather, 
before its prognostications will commonly be understood ; for 
a rise may foretel an abatement of wind, — a change in its 
direction, — or the return of fine weather; or if the wind is 
light and variable, it may foretel its increase to a steady 
breeze, especially if there is any easting in it ; and a fall may 
prognosticate a strong breeze or gale, a change of wind, the 
approach of rain, or the dying away of a steady breeze. 
Most seamen are tolerably good judges of the appearance of 
the weather ; and this judgment, assisted by observation upon 
the quick or slower rising or falling of the mercury, and 
upon its relative height, will in most cases enable them to fix 
upon which of these changes are about to take place, and to 
what extent, where there is only one ; but a combination of 
changes will be found more difficult, especially where the 
effect of one upon the barometer is counteracted by the other ; 
as for instance, the alteration of a moderate breeze from the 
westward with dull, or rainy weather, to a fresh breeze from 
the eastward with fine weather, may not cause any alteration 
in the height of the mercury ; though I think there would 
usually be some rise in this case. Many combinations of 
changes might be mentioned, in which no alteration in the 
barometer would be expected, as a little consideration, or 
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