MARINE BAROMETER. Igl 



Sphere, where the effect of sea and land winds upon the bare- ^, 

 *^ . ■* Observations 



meter is likely to be the most conspicuous. and inferences 



In the open sea, the mercury seems to stand higher in a ^^ ascertain th« 

 steady breeze of several days continuance, from whatever changes of 

 quarter it comes, provided it does not blow hard, than when wind and wea- 

 ihe wind is variable from one part of the compass to another ; pi^'j' j° after^* 

 and perhaps it is on this account, as well as from the direction change in the 

 of the wind, that the mercury stands higher within the tropics, rn^"ne baro- 

 than, upon the average, it appears to do in those parallels 

 where the winds are variable and occasionally blow with vio- 

 lence. 



The barometer seems capable of affording so much assistance 

 to the commander of a ship, in warning hira of the approacht 

 and termination of bad weather, and of changes m 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 be always 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 

 foretelan 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 afiy alteration in the height of 

 the mercury ; though I thjnk there would usually be some rise 

 in this case. Many combinations of changes might be men- 

 tioned, in which no alteration in the barometer would be ex- 

 pected, as a little €onsidcration, or experience in the use of 



S 3 this 



