24 THE EUROPEAN STORM OF DECEMBER 21-28, 1836. 



The fall of the Barometer in Great Storms is not the effect of Centrifugal Force. 



Some persons have imagined the fall of the barometer in a storm to be due to 

 centrifugal force. They say " the atmosphere constituting the body of the storm is 

 driven outward from the centre towards the margin, just as water in a pail which 

 is made to revolve rapidly flies from the centre and swells up the sides." But 

 according to the principles of mechanics, the centrifugal force of a body revolving 

 in a circle is to its weight as V' to 32 B, Avhere V represents the velocity in feet 

 per second, and R is the radius of the circle expressed in feet. Now, on the 25th 

 of December the barometer fell half an inch below its mean height throughout a 

 circle whose radius was 400 miles. 'We will estimate the velocity of the wind at 

 70 miles per hour, or 100 feet per second. Then 



C : W : : 10000 : 32 x 400 x 5280 

 or C: TF:: 1 : 6758; 



that is, the centrifugal force is less than g-^^-^ part of the weight of the revolving 

 body — a force which would depress the barometer less than ^^-^ of an inch, whereas 

 the barometer actually fell a half inch below its mean height ; in other words, the 

 centrifugal force generated by the rotation of the wind had no appreciable influence 

 on the state of the barometer. 



Supposed connection between the American and European Storms. 



The European storm of December 25, 1836, was entirely independent of the 

 American storm of December 20th. The rate of progress of the American storm 

 of December 20th was such that it could not have reached England before the 

 27th ; whereas the European storm had become fully organized on the 23d, and 

 tlie first movement of the storm can be distinctly traced in Germany on the 22d. 

 The European storm evidently originated in Europe ; and the American storm 

 gradually wasted away, and probably could not be traced beyond the middle of the 

 Atlantic. 



Generalizations. 



By comparing the European storm of December 25, 1836, with the American 

 storm of December 20, 1836, and also the storms of February 4 and 16, 1842, of 

 which I have published an investigation in the Transactions of the American Phi- 

 losophical Society, vol. ix. pp. 161-184, we are led to the following generalizations. 

 Some of these conclusions are substantially the same as given by Mr. Espy, in his 

 Fourth Meteorological Report ; but several of Mr. Espy's conclusions are only true 

 when applied to American storms. 



1. The area covered by a violent storm of rain or snow is sometimes nearly 

 circular in form ; sometimes its form is very much elongated or elliptical, its length 

 being two or three times its breadth ; and frequently its form is very irregular. In 



