DISCUSSION AND ANALYSIS OP WINDS. 6(U 



appreciable movement could be observed. All this lessens the value of the 

 observations on motion of clouds. 



Generally it is seen, that the clouds move from the same direction as the air 

 near the surface of the earth, which would lead to the conclusion that the lower 

 strata of clouds were those observed. 



As to the higher clouds, the cirri, as far as known, they move generally from 

 the west, except in the polar regions. 



Considering all this, as well as the fact that the motion of clouds is recorded 

 in this work for very few places outside of the United States, I shall not consider 

 the subject in the further deductions, leaving to every one interested to draw 

 his own conclusions from the tables and the map, Plate 1. 



The most important works in meteorological science in the last twenty-two 

 years are devoted to the proof of the mutual dependence of atmospheric pressure 

 and winds. 



It has for a long time been admitted that in the belts of the trade-winds the air 

 moves from the regions where pressure is high (the polar limits of the trades) 

 towards the low pressure of the equatorial regions. The phenomena here were so 

 simple and regular that the explanation was very easy. In the case of the tropical 

 hurricanes it was also generally admitted that the wind blew towards the low 

 pressure in the centre of the storms. The meteorological phenomena of the 

 temperate and polar regions are much more complicated, and the causes of them 

 less easily detected. 



It was Prof. Buys-Ballot who proved the general dependence of the winds on 

 the pressure of the air. In its original enunciation, his celebrated law of the luinds 

 declares that the winds will blow from the region where the barometer is above 

 the mean towards that where it is below, and will be deflected 60° to 80° towards 

 the right, owing to the rotation of the earth. He subjected this law to a severe 

 practical test in using it in the system for prediction of storms which had been 

 established at that time in the Netherlands. Buys-Ballot's law of the winds is 

 now very generally accepted, though in a somewhat modified form, viz. : tlie icind 

 blows from a region of high pressure towards one of loio pressure, an / is deflected 

 to the right owing to the rotation of the earth. In 1853, Prof. Coffin arrived at a 

 very similar conclusion, saying, " that in the northern hemisphere a wind arriving 

 from its mean direction always finds the point of maximum pressure on its left, 

 and the minimum to its right ; while the reverse is true in the southern hemi- 

 sphere. There seem to be no exceptions to this law." He further states {Pro- 

 ceedings of American Association, 1853, p. 88) that the deflection in this case is 

 65° ; that is, very near to that found by Dr. Buys-Ballot. Even before Professor 

 Cofiin, Espy expressed similar views, as seen in his " Philosophy of Storms" and 

 "Meteorological Reports." Very likely the views of the American meteorologists 

 were too much in advance of their time to be generally accepted. When Dr. 

 Buys-Ballot published his law of the winds, meteorology had made much more 

 progress, so as to render such views more easy of acceptance. 



Tliis law applies to storms as well as gentle winds, to single hours of obser- 

 vations as well as to monthly and yearly means. 



