SHORT MEMOIRS 0!^ METEOROLOGICAL SUBJECTS. 465 



K. 



ON THE EELATION BETWEEN BAROMETRIC VARIATIONS 

 AND THE GENERAL ATMOSPHERIC CURRENTS. 



By Mr. Peslin, Mining Engineer at Tarbes. 



fFrom the Bulletin International de I'Obs. de Paris et de I'Obs. Phys. Cent, de Montsonris, 1872, May CO 

 to July 7, inclusive. Translated by Cleveland Abbo.] 



(1) The Laws of the ^Yin(ls given by the Synoptic Weather Charts. 



If we study the synoptic charts that the Imperial Observatory at 

 Paris has collected in the " Atlas of the General Movements of the 

 Atmosphere," we are struck by the generality of a fact which, at first 

 thought, seems contrary to the laws of mechanics. The atmospheric 

 currents never move in a direct line from the region of high barometric 

 pressure toward the region of low pressure; but, according to the numer- 

 ous observations recorded in the synoptic charts, the direction of the 

 wind is more often nearly that of the tangent to the isobarometric 

 curves. One might conclude from this that the variations of atmos- 

 pheric pressure have little or no influence upon the direction of the 

 wind ; that the movements of the terrestrial atmosphere are regulated 

 by some foreign force, which has no relation to the pressure indicated 

 by the barometer. 



However, a more thorough examination of the synoptic charts enables 

 us to recognize a certain co-relation, on the one hand, between the 

 direction of the atmospheric currents and the direction of the baro- 

 metric variations, counted normally, to the current, and, on the other 

 hand, between the force of the wind and the rapidity of this transverse 

 variation of the pressure. For the sake of clearness, let us personify 

 the wind, and suppose that Eolus faces always toward the point of the 

 horizon toward which he blows. We shall perceive, in the first place,, 

 that in the synoptic charts the high barometric pressures are always on 

 his right hand, and the low pressures on his left hand. In the second 

 place, we shall see that when the synoptic chart shows regular and vio- 

 lent winds over a certain extent of country, the isobars cross over this 

 region, and traverse it in parallel lines close together. 



According to the examination that we have been able to make of the 

 published synoptic charts, the preceding laws are very general, and 

 can be safely applied to the whole temperate zone of our hemisphere;, 

 they are a simple extension of known laws of the movements of the air 

 in cyclones and tempests. We shall now seek to give their explana- 

 tion accoiding to the principles of mechanics. 



(2) Mechanical Conditions of the Existence ofati Atmospheric Current. 



I assume that some cause initiates in our hemisphere a general 

 atmospheric current; that is to say, a current of air following a con- 

 stant direction over a large extent of country. I will now seek the 

 30 s 



