106 Lieut.-Col. Sabine's Report on the Meteorology of Toronto. 



much nearer to an equality in the two seasons of summer and winter, than do 

 those of the barometer. A north-west wind at Toronto is usually accompanied 

 by a rise in the barometer and a fall in the temperature with a diminution in 

 the tension of vapour ; and a south or south-east wind, by a fall in the baro- 

 meter and a rise in the thermometer with an increased tension of vapour. 

 In a change from one of these winds to the other, consequently, the alteration 

 of the gaseous pressure would be greater than that of the barometric pressure, 

 which is partially counteracted by the accompanying change in the elastic 

 force of the vapour :.• and as already noticed, the fluctuations in the vapour 

 pressure are very considerable in summer. I have selected some remarkable 

 instances in a single year, 1841, which are as follows: — 



Variations of Vapour Pressure in 1841. 



d, h. 



Between May 30 16 and June 



„ June 11 „ June 



„ June 30 2 „ July 



„ July 2 6 „ July 



„ July 23 4 „ July 



„ Aug. 18 2 „ Aug. 



If the principles are correct, of which we have here traced a portion of the 

 consequences, barometrical observations generally must lose an essential part 

 of their value when unaccompanied by hygrometrical observations, by means 

 of which the pressures of the air and vapour may be separated. Whenever 

 such complete observations are made, i. e. hygrometric as well as barometric, 

 the tension of vapour should be computed on the spot and at the instant. 

 When calculations of this nature are suffered to fall in arrear, unreduced 

 observations accumulate, and danger is incurred that the calculations are 

 never made, and that science will lose the advantage which the observations 

 were capable of affording. 



The comparison of the barometric range in the different months at Toronto 

 and Prague exhibits a very satisfactory accordance, and shows how similar 

 are the phaenomena which present themselves in this respect over the two 

 continents. 



The comparison of the range of the vapour pressure at Prague and Toronto 

 exhibits only such differences as may be reasonably ascribable to the greater 

 range of the temperature at Toronto, and possibly to the greater facility with 

 which the air can acquire vapour at that station from the great lakes in its 

 vicinity. 



It may be worthy of notice, that the highest and lowest barometric obser- 

 vations in the two years at Toronto occurred within a very few days' inter- 

 val of each other, being apparently parts of one great atmospheric wave. 



The highest and lowest barometric observations at Prague also took place 

 within a few days of each other, and at the same season, viz. midwinter, but 

 a year earlier. The observations were as follows, viz. — 



Extreme Range of Barometer in 1840, 1841. 

 Toronto. Prague. 



Max. Dec. 22, 1841 .... 30-417 Dec. 27, 1840 .... 30-260 

 Min. Dec. 4, 1841 ... . 28-672 Jan. 4, 1841 .... 28-654 



Interval 1 8 days. .. . 1-745 Interval 9 days 1-606 



W^e have undoubtedly made a considerable step in advance in meteorology, 

 if we thus correctly substitute the consideration of the separate daily march of 

 the pressures of the vapour and of the gaseous atmosphere, for the compara- 



