Prof. J. P. Espy on the Law of Storms. 345 



was given to the agent ; what other agent held it ? Also what 

 becomes of B ; what new agent holds it ? Suppose the weight 

 was raised by the action of steam^ we trace it back to the force 

 engendered by the chemical action of the fuel combining with 

 oxygen. The force of the chemical action is transferred to the 

 molecules of water and makes its appearance as molecular vis 

 viva. Before the chemical action, the relation of A to the mole- 

 cules about to combine is similar to tlie relation of force to a body 

 about to fall from a height. The force about to be given is con- 

 cealed in an agent, a medium, the instrument of chemical or 

 electric force ; is evolved from it, and returns to it again when 

 the products of combustion are decomposed at a future time. 



Thus may every appearance in nature be viewed as the exhibi- 

 tion of a part of a cycle of dependent action; and we have reason 

 to be impressed vidth the necessity of keeping the dynamical 

 aspect of a phsenomenon in view, if we desire to explore its rela- 

 tions with others, and its place in the general scheme. 



Edinbiu-gh, March 18, 1858. 



XLIII. On the Law of Storms. By Prof, James P. Espy. 

 To W. Francis, Esq. 



Sir, "Washington City, March 9, 1858. 



I SEND you this paper, not for the purpose of demonstrating 

 anything, but to induce the various learned bodies in your 

 country, especially those which are engaged at present in similar 

 investigations, to take up the subject and examine whether the 

 wind, as I maintain, blows in towards the centre of great storms, 

 hurricanes, and tornadoes, according to the evidence furnished 

 in my ' Fourth Report ' on Meteorology herewith sent to you. 



I have now examined 170 storms as they pass over the United 

 States from west to east, of which 100 were given in the pre- 

 ceding Report, and more than fifty in this, from which I have 

 drawn more than twenty generalizations, of which the first three 

 are the following : — 



The rain- and snow-storms, and even the moderate rains and 

 snows, travel from the west towards the east in the United 

 States. 



The storms arc accompanied with a depression of the baro- 

 meter near the central line of the storm, and a rise of the baro- 

 meter in front and rear. 



This central line of rainiumni is, in the cold months, of great 

 length north aud south, and travels with the storm towards the 

 cast, side foremost. 



Phil. May. S. 4. Vol. 15. No. 101. May 1858. 2 A 



