538 



METEOROLOGY. (OCEAN METEOROLOGY.) 



of a friend who witnessed the phenomenon. It oc- 

 curred at a point on the Susquehanna river where 

 the western approach is a long gradual slope, 

 while on the eastern side the halls are high and 

 abrupt. The tornado cloud was seen coming from 

 the west, gathering force as it came, till within a 

 short distance of the eastern shore, when a per- 

 ceptible change took place in its form, consequent 

 on the shutting off of the currents of air from 

 the east. The spiral column being thus deprived 

 of one of its supports gave way, its base was 

 broadened, and there came a " cloud-burst." The 

 other incident was observed by the author him- 

 self. The cloud was coming down the south side 

 of a narrow valley. Passing a small piece of 

 timber, mostly lying on the south of its track, it 

 swerved a little to the south, and was brought 

 opposite a sharp hill on the north side of the val- 

 ley and about 300 yards away. It then turned al- 

 most at a right angle to its former course, directly 

 toward the hill, on which it destroyed a barn, 

 some out-buildings, and several trees. It then 

 resumed its original course, much more feebly 

 than before. 



From the facts adduced in his papers on 

 " Trombes and Tornadoes," M. Faye concludes, 

 that there are no centripetal movements, either 

 at the foot of trombes or tornadoes or toward the 

 base of cyclones ; and that trombes, tornadoes, 

 typhoons, and cyclones are varieties of the same 

 mechanical type, of which the analogy may be 

 found in water courses. They are descending 

 whirls with vertical axes originated in the upper 

 currents of the atmosphere, and follow the direc- 

 tion of those currents. This proposition, Mr. 

 Faye adds, is not his, but wa? made a century 

 ago by Dr. Parkins, of Boston, in a letter to 

 Benjamin Franklin. 



For many years Prof. J. Hann has maintained 

 the theory that cyclones and anticyclones have 

 their origin in the circumstances of the general 

 atmospherie circulation, and are not primarily 

 due to the heating or cooling of that part of the 

 earth's surface which they temporarily occupy. 

 From time to time he has had this view, and the 

 views which logically grow out of it, confirmed 

 by observations at high mountain stations. From 

 the results of such observations, he says, in his 

 latest memoir, " we must now conclude that the 

 temperature conditions of wandering cyclones 

 and anticyclones are the effect and not the cause, 

 that they are the consequence of the movements 

 of the air masses, of the ascents and descents of 

 the vertical circulation of the atmosphere. There 

 can no longer be any doubt that the pressures in 

 barometric maxima and minima generally are to 

 be explained mainly through these movements of 

 the air. The forces which set up the atmospheric 

 circulation of the higher latitudes, especially in 

 winter, have their origin in the warmth of the 

 tropics that is to say, in the difference of tern- 

 perature between the polar regions and the tem- 

 perate zone. Cyclones and anticyclones are but 

 partial phases in the general circulation of the 

 atmosphere. The air currents that set toward 

 the poles as a consequence of the upper gradients 

 are partially resolved in vortices in the high'er 

 latitudes, and their progressive movement is 

 chiefly determined by the prevailing westerly 

 direction of the wind currents. The influence of 

 variations of the terrestrial surface, of the li oat- 



ing and cooling of continents and oceans, as well as 

 of the local influx of water vapor and its conden- 

 sation, are but of secondary importance." 



Kiersnowski's investigations of the daily and 

 yearly variation and the distribution of wind ve- 

 locities in the Russian Empire show that the 

 highest velocities (6'3 metres per second) occur 

 in the Baltic provinces. The velocities are also 

 high on the White Sea and the Caspian, in the 

 region of the north Russian lakes, and on the 

 steppe, while they are low in the forest region 

 and the Caucasus. They decrease toward the in- 

 terior of Asia, and reach their minimum (1-5 me- 

 tre per second) in the Transbaikal. Further 

 east, toward the Pacific, the velocity increases. 



Ocean Meteorology. The first attempt to 

 deal with the diurnal phenomena of meteorology 

 over the ocean is made in the meteorological " Re- 

 port of the Challenger Expedition," which has 

 been prepared by Dr. Alexander Buchan. Tem- 

 perature, pressure, and movements of the atmos- 

 phere, together with such phenomena as squalls, 

 precipitation, lightning, and thunder storms, are 

 discussed in it. It was found that in equatorial 

 and subtropical regions the mean temperature 

 of the surface of the sea falls to the daily mini- 

 mum between 4 and 6 o'clock A. M., and rises to 

 the maximum between 2 and 4 o'clock p. M., the 

 amount of the diurnal variation being only 0'9 

 F. In the higher latitudes of the Antarctic 

 Ocean the diurnal variation was only 0'2. Of 

 the four great oceans, the greatest variation was 

 1, in the north Pacific, and the least 0'8, in the 

 Atlantic. The diurnal phases of the temperature 

 of the air over the open sea occur at the same 

 time as those of the temperature of the surface, 

 but the amount of the variation is about 3, ris- 

 ing near land to 4'4. The greater variation of 

 the temperature of the air, as compared with that 

 of the surface of the sea on which it rests, is a 

 point of much interest from the important bear- 

 ings of the subject on the relations of the air and 

 its aqueous vapor in its gaseous, liquid, and solid 

 states, and the particles of dust everywhere pres- 

 ent, to solar and terrestrial radiation. Thus the 

 air rises daily to a higher, and falls to a lower 

 temperature than does the surface of the sea on 

 which it rests. The diurnal variation of the elas- 

 tic force of vapor in the air is seen its amplest 

 form over the open sea, where the curve is close- 

 ly coincident with the diurnal curve of tempera- 

 ture. But near land the elastic force is depressed 

 instead of rising at noon and 2 p. M., and indi- 

 cates double maxima and minima. The diurnal 

 oscillations of the barometer appear, from the 

 phenomena they present, to be caused, primarily, 

 by the direct heating by solar radiation and cool- 

 ing by terrestrial radiation of the molecules of 

 the air and its aqueous vapor, and the changes 

 consequent on that cooling. It follows that 

 these changes of temperature are instantly com- 

 municated through the whole atmosphere, from 

 its lowermost stratum resting on the surface to 

 its extreme outer limit. The velocity of the 

 wind appears to be greater by four or five miles 

 an hour over the open sea than at or near the 

 land, and practically no diurnal variation was ob- 

 served in the wind's velocity over the open sea ; 

 while near land the velocity gives a curve, with 

 a minimum between 2 and 4 A. M. and a maxi- 

 mum between noon and 4 p. M. The diurnal 



