Mean Pressure of the Atmosphere in Diffa-ent Latitudes. 469 



height of the barometer at London has been reduced to 27'83 

 inches, as before mentioned, and 30*70 inches is an elevation, 

 which, at any rate, has been very Uttle exceeded in this coun- 

 try ; but from the observations of M. Kupffer*, it appears 

 that at St, Petersburgh the greatest depression of the barome- 

 ter, during thirteen years, was to 28*35 inches, and the great- 

 est elevation was 31*29 inches. 



It is obvious that the nearer we approach the atmospheric 

 columns of least height, the smaller must be the quantity of 

 air which can flow from their tops, and the greater that which 

 can be accumulated upon them ; so that the degree in which 

 their pressure may be diminished is lessened, and their capa- 

 bility of receiving additions to it is increased. 



I think I have now noticed the whole of the more import- 

 ant atmospheric phsenomena connected with the height of the 

 barometer at the surface of the earth, excepting the horary 

 variations of this instrument ; but these evidently arise from 

 a distinct cause, which, there can be little doubt, is the disturb- 

 ance given to the balance of the two currents by the alternate 

 heating and cooling of the air during day and night, as has 

 been set forth by Professor Daniell. 



LXVIII. On the Differences of the mean Pressure of the At- 

 mosphere on different Latitudes. By William Brown, 

 Jun.f 



IN the foregoing paper I have attempted to show, that the 

 oscillations of the barometer are caused by the opposition 

 presented by the descending equatorial current of the atmo- 

 sphere, to the influx of air from higher to lower latitudes. 

 When that paper was written, I was not aware of the obser- 

 vations collected by M. Shouw, showing the differences which 

 exist in the mean height of the barometer at different latitudes. 

 The original essay in which these are given, published in the 

 Comptes Rendus des Seances de V Academic, 1 have not seen ; 

 but it is referred to in the ' American Journal of Science ' 

 for October 1841, by Professor Loomis, who has extracted 

 from it a table containing his results ; the height of the baro- 

 meter being corrected for the differences in the force of gra- 

 vity. 



Now allowing for errors of observation, the numbers in this 

 table representing the height at various places on the same 

 latitude, agree too well with each other, and the almost un- 

 disturbed order of the variations is too well marked, to admit 



• Edinburgh Philosophical Journal, 1840. 

 t Communicated by the Author. 



