﻿440 Mr. J. K. Laughton on Barometric Differences 



storm, in the tropics as well as outside, the wind on the eastern 

 side is equatorial, is warmer and more humid than the polar 

 air on the western side; and the amount of rain in a storm 

 within the tropics is almost beyond comparison greater than 

 that in a storm of higher latitudes. If the difference of tem- 

 perature and the condensation on the eastern side of the area 

 of least pressure could occasion the movement towards the east 

 in temperate or high latitudes, much more could they do so in 

 low. But Mr. Buchan conceives that if the progressive move- 

 ment of a storm were due to the direction of a ruling wind, the 

 velocity of the storm-wind would be greatly modified in the 

 different quarters of the revolution — and that whilst (if the 

 storm were moving towards the east) it would be very much in- 

 creased on the south side of the centre of depression, it would, 

 on the contrary, be very much diminished on the north side. 

 To illustrate this, he supposes an extreme case of a storm in 

 which the velocity of the wind is twenty-five miles an hour, and 

 its rate of progression towards the east the same ; and argues 

 that there would be an absolute calm* at any place on the north- 

 ern side of the revolution*. I see no reason why in such a case 

 there should not be such a calm ; but it is not customary either 

 amongst meteorologists, or among sailors, whom storms more 

 personally affect, to speak of a wind of twenty -five miles an 

 hour as a storm ; but a whirl in which the wind has a velo- 

 city of fifty or sixty miles, and which is travelling eastwards at 

 the rate of twenty or thirty miles an hour, may very well appear 

 on its northern side as a wind of thirty or forty miles an hour, 

 and on its southern side as a storm of seventy, eighty, or even 

 ninety. The results of the observations which Professor Mohn 

 has so carefully accumulated offer no contradiction to such a 

 view, but, indeed, very strongly support it, as they lead him 

 (although adhering to the purely meteorological theory) to 

 estimate the frequency of storms in the southern and northern 

 halves of these circles revolving round a centre of depression as 

 in the ratio of 38 : 22, or very nearly 2 : 1 f. 



But if the storms are carried along in the body of the pre- 

 vailing wind, they stand to it in exactly the relation that whirls 

 of water do to the stream that sweeps them down ; they exercise 

 no more general influence on the wind than these do on the 

 course of the river ; and the onward flow of the one, as the 

 downward flow of the other, is quite irrespective of these minor 

 though frequently important disturbances. 



The wide application of the very ingenious law proposed by 

 Professor Buys-Ballot is apt to mislead those who trust too ex- 

 clusively to meteorological, as opposed to geographical observa- 

 * Handy Book, p. 286. f Atlas des Tempetes, p. 12. 



