1834.] 



liemarks on the Marine Barometer. 



170 



aware that its construction originated in a discovery, that the mean 

 density of the atmosphere is capable of supporting a column of 

 mercury equal to about thirty inches in length, hence it follows that 

 every deviation of the quicksilver from this height, is the result of a 

 correspondent chani2:e, in the actual gravity of the surrounding 

 atmosphere, the trifling effect of the cohesive properties of the tube 

 being duly allowed for. But although this may be sufficiently 

 evident to a common observer, it is certain that these changes 

 depend upon so many hidden causes, and are generally so minute 

 that they are scarcely perceptible to the eye, and are frequently 

 unaccompanied by any visible change of the weather. It is a well 

 established fact, that the Barometer undergoes but little or no varia- 

 tion throughout the region of the tropics, unless when it happens to 

 be under the influence of an approaching hurricane, and then it is 

 no less certain that the quicksilver falls rapidly and considerably, 

 a natural consequence it would seem, of the origin of these storms, 

 "which exceed in violence those of the more boisterous climates of 

 Europe, as much as the situations in which they are generated, 

 at other times exceed them in mildness. An infinite scope still 

 remains for a philosophical inquiry into the theory of winds, nor 

 have 1 yet met with any satisfactory explanation of the course of 

 these awful phenomena in the heavens. If I may presume to ven- 

 ture an opmion on so abstruse a subject, I should say that a tropical 

 hurricane is produced by the rays of a vertical sun acting upon 

 some portion of the atmosphere that happens to be unusually loaded 

 with the electric matter so abundantly generated within a few 

 degre s of the equator, whereby a rapid rarefaction of the circum- 

 jacent atmosphere takes place, repelling in its escape the surrounding 

 air, until the existing cause has exhausted its influence, when a 

 reaction commences, by the condensed air rushing towards the 

 centre of the atmospheric rarefaction until the equilibrium is 

 restored. 



If this theory should prove to be well foundedy it would, perhaps, 

 sufficiently account for the great and sudden falling of the quick- 

 silver on such extraordinary occasions ; but, as Dr. Franklin very 

 justly observes, in his Treatise on Electricity, " it is not of much 

 importance to know the manner in which nature executes her laws ; 

 it is enough if we know the laws themselves so it may be said, 

 that on all these occasions, whatever may be the immediate cause 

 of the fall, provided we are aware of what is to follow, we are fur- 

 nished with all the requisite information to guard us against the 



