William Ferrel

“ As friction is a very important element in calculations of the motion of the atmosphere, and its effect cannot be determined, it would be impossible to calculate the motion of the atmosphere from the forces which act upon it, if they were even accurately known. ”

“ That they may receive their origin and first impulse in this way, we think is very probable; but that violent hurricanes, extending over a circular area nearly one thousand miles in diameter, and continuing for ten days, and proceeding with increasing violence from the torrid zone to high northern latitudes, depends upon any primitive impuls alone, we think is very improbable. For if even any part of the atmosphere should receive such an impulse as to pruduce a most violent hurricane, friction would soon destroy all motion and bring the atmosphere to rest. ”

“ A second force arises from the tendency which the atmosphere has, when, from any cause, it has risen above the general level, to flow to places of a lower level. These two preceding forces generally produce counter-currents. Again, when, from any cause, a particle of air has been put in motion toward the north or south, the combination of this motion with the rotatory motion of the earth produces a third force, which causes a deflection of the motion to the east when the motion is to the north, and a deflection to the west when it is toward the south. ”

“ The ocean not level. - As it has been shown in the case of the atmosphere, that the resultant of the forces causes an accumulation about the parallels of 28°, so as the motions of the ocean are somewhat similar, and it is acted upon by the same forces, it may be shown that there must be a slight accumulation about those parallels in the ocean also. Whatever may be the causes of the motion of the ocean, we know that in the torrid zone it has a small western motion, and in the other parts a slight motion towards the east. ”

“ Besides, no gradually accelerated motion can depend upon a primitive impulse alone, even where there is no friction. Hurricanes then, and all ordinary storms, must begin and gradually increase in violence by the action of some constantly acting force, and when this force subsides, friction brings the atmospher to a state of rest. This force may be furnished by the condensation of vapor ascending in the upward current in the middle of the hurricane, in accordance with Professor Espy's theory of storms and rains. ”

“ If we now suppose that the greater specific gravity alone of the atmosphere at the poles, is sufficient to cause the barometer to stand one inch higher there than at the equator, which would only require a difference of temperature of about 16°, it would still leave a difference in the height of the barometer between the poles and the equator about equal to the observed difference in the southern hemisphere. ”

“ We shall now undertake to show that there cannot be a rushing of air from all sides towards a center, on any part of the earth except at the equator, without producing a gyration, and that the tendency to a distinct kind of gyration in each hemisphere, is owing, neither to any pecularities of the winds or aerial currents, nor to the mysterious agent of magnetism, bu that it results, as a necessary consequence, form the action, upon the atmosphere, of the four forces which we have taken into consideration in the first part of this essay. ”

“ Now we may judge how exceedingly small a current this would produce when we consider that there is a rise of about two feet in the open ocean at one place and a fall of the same amount at another every six hours, caused by the tides, and yet the flowing of the water from the one place to the other place to produce this rise at one place, and fall at the other, it is well known does not produce any sensible currents in the open sea. ”

“ The fact that Ehrenberg has discovered South American infusoria in the blood-rains and "sea-dust" of the Cape Verde Islands and other places, does not prove the crossing of the winds; for, according to the explanation of the winds given above, there are two curents flowing into each calm-belt, and also two flowing out in opposite directions, as it were from a common reservoir, and, consequently, whatever is carried into these belts from either side down flow out again in each direction; and so infusoria in one hemisphere can easily pass to the other without a distinct crossing of the currents. ”

“ In consequence of the atmosphere's revolving on a common axis with that of the earth, each particle is impressed with a centrifugal force, which, being resolved into a vertical and a horizontal force, the latter causes it to assume a spheroidal form conforming to the figure of the earth. ”

“ We think it, therefore, manifest that neither evaporation nor the salts of the sea can have much influence in producing currents, even upon Lieutenants Maury's hypothesis, that evaprotation is greatly in excess of precipitation in the torrid zone. But is this a true hypothesis? Although there is a great evaporation in the torrid zone, there is also great precipitation ”

“ Hence, at a certain distance from the center the hurricane has the greatest violence, and within this circumference, friction in a great measure destroys the gyrations, so that the middle of our most violent hurrianes is a calm. ”

“ But, as the portion of the atmosphere having a relative eastern motion, is nearer the axis than that which has a relative western motion, and as the part having a western motion, inasmuch as it is further from the axis, must be somewhat less than the part comprised between these parallels, in order to make the products equal, unless the relative velocity of the part having an easterly motion is very much greater. ”

“ According to this theory, all storms are produced by an ascending current of warmer atmosphere above by means of the caloric given out of the vapor which is condensed as it ascends to colder regions above. Therefore, as long as this ascending current can be supplied with air saturated with vapor this continual rarefaction must take place, and also the ascent of the air from all sides to supply its place. If, then, all the lower stratum of atmosphere over a large district were saturated with vapor, without some disturbing cause, it might remain undisturbed ”

“ In like manner the air at N when there is any force which tends to make the surrounding air flow towards a center, the resultants of all the forces which act upon it must cause it to receive a gyratory motion, and that this motion in the northern hemisphere must be sinistrorsal, but in the southern hemisphere the contrary. ”