39 



mometnc disturbance; not points of maximum or minimtim temperature 

 absolutely, for we only regard the deviation from the mean temperature of 

 the place for the given hour and month. These barometric and ther- 

 mometric curves exhibit some conformity to each other, but are far from 

 being identical. The direction of the \vind is represented by arrows, and 

 its force is indicated, so far as convenient, by their length.* 



Other phenomena are now indicated by colors. Those regions where 

 the sky was unclouded, or where the cloudiness was less than one- half, 

 are colored blue; those where the sky was entirely overcast, or the cloudi- 

 ness exceeded one-half, but without rain or snow, are colored brown. 

 Those regions upon which snow is falling, are colored green ; and those 

 where rain is foiling, are colored yellow. Thus, nearly every important 

 circumstance of a storm is presented to the eye at a single glance. All 

 these particulars will be understood from the two accompanying charts, 

 illustrating the progress of the storm of February 16, 1842. 



In both the storms of February, 1842, after they had acquired consider- 

 able violence, there was a prevalent motion of the winds inward, with a 

 tendency to circulate around the centre, in a direction contrary to the sun's 

 motion. The motion of the wind, therefore, was neither wholly centrip- 

 etal nor wholly rotary, but a combination of the two. As long as the 

 wind was moderate, neither of these tendencies was ciearly marked, and 

 there were numerous perplexing anomalies, probably occasioned in many 

 instances by the inequalities of the earth's surface. The storm of Febru- 

 ary 16 travelled in one day 560 miles in a direction N. 53° E., making its 

 velocity 23 miles per hour. The storm of February 1-5 remained for 

 two days nearly stationary, and then travelled N. 62° E. at the rate of 36 

 miles per hour. On the whole, then, we may conclude that when storms 

 are violent, and there is a great depression of the barometer, the direction 

 of the wind presents considerable regularity, being spirally inward towards 

 the centre of the storm; but when the winds are moderate, which is the case 

 of most frequent occurrence, this tendency is very fully developed, and 

 the subject demands more particular investigation. 



III. I now proceed to inquire what encouragement there is to a further 

 prosecution of meteorological researches. 



In all our investigations respecting natural phenomena we assume that 

 the operations of nature are subject to laws, and that these laws are uni- 

 form in their operation. A law of nature knows no exceptions. There 

 is no place for science except upon this basis. Are storms subject to laws, 

 and are these laws invariable? Such a question may appear almost like 



*For an account of the method employed by Mr. Espy in representing the phases of storms, 

 see his communication, appendix No. 3. 



