ON THE METEOROLOGY OF TORONTO IN CANADA. 57 



In these last remarks I have perhaps ventured further from the strict sub- 

 ject of this communication than I should have been disposed to have done, 

 had I not had in view to call the attention of the Section to what it is in the 

 power of our own countiy to accomplish, Avith its widely extended dominions, 

 in the solution of this great problem of the uniformity or otherwise of the 

 mean pressure of the atmosphere, by the establishment of colonial observato- 

 ries, conducted on a systematic plan, and continuing in operation only until 

 certain specified and definite objects should be attained ; such, for example, 

 as the mean values, and the periodical variations, of the several meteorological 

 elements. The present communication is an evidence of the important re- 

 sults which even a very brief duration of such observations may be sufficient 

 to accomplish. When such establishments are proposed, with the sanction 

 and support of the colonial authorities, and with the advantage of men of 

 assured competency to conduct them, we may venture to promise the fullest 

 co-operative aid (that may be compatible with circumstances) on the part of 

 the British Association, which has placed foremost amongst its objects " to 

 give a stronger impulse, and a more systematic direction to scientific inquiry." 



I have one more point to bring under your notice ; a point highly inter- 

 esting in itself, and completing the evidence of the harmony in the meteo- 

 rological variations. 



It has been noticed that from the diminution of the gaseous pressure as 

 the temperature of the day increases, evidencing an ascending current, we 

 should be prepared to expect a corresponding influx of air at the station, or 

 a diurnal variation in the force of the wind (taken without reference to the 

 direction from which'it blows), which should have its minimum at or near the 

 coldest hour of the day, and its maximum at or near the warmest, and its pro- 

 gression in harmony with the curve of temperature, having one ascending and 

 one descending branch. Such is the fact. The subjoined table exhibits the 

 sum of the pressures, expressed in pounds avoirdupois, exerted on a square foot 

 of surface at Toronto, at each of the observation hours in ISil, and the same 

 in 1842. The wind is proverbially uncertain, and our means of measuring its 

 pressure are more imperfect than we could desire ; but these numbers afford 

 an ample evidence that there is a diurnal variation in the force of the wind, 

 and furnish a curve which, when projected, is found in remarkable corre- 

 spondence with the curve of the temperature. This fact, observed at Bir- 

 mingham by Mr. Osier, has been already brought under the notice of the 

 Association at a former meeting. The diurnal march of the gaseous atmo- 

 sphere furnishes the additional link in the chain of evidence, by which the 

 connexion between the temperature (producing an ascending current) and the 

 force of the wind (flowing in to replace it) may receive its explanation ; 

 placing before us in an intelligible form their mutual relations to each other, 

 as cause and effect. 



necessary to regard the influence of the season of the year (summer) at which the barometer 

 was observed at Port Famine ; as well as the correction due to the effect of the variation of 

 gravity on the standard of measure. Both corrections would tend to increase the mean 

 pressure of the gaseous atmosphere at Port Famine in comparison with that at the Equator. 

 The barometrical obsen'ations made in the Erebus, in the late Antarctic Expedition, furnish 

 a beautiful illustration of the progressive decrease in the height of the barometer from the 

 tropics to the high latitudes, coincident with the diminution of the elastic force of the vapour 

 accompanying the decrease of temperature. I hope that Sir James Ross will shortly pubUsh 

 these interesting observations, with the corresponding pressures of the gaseous atmosphere in 

 the different parallels. 



