110 ABNORMAL VARIATIONS AT TORONTO. 



days give the daily rate of change independently of the effect of 

 regular periodic diurnal variation, though affected it may be by the 

 hour chosen, should the element be systematically more liable to 

 disturbance at one hour than another 



As the normal temperatures for the same hour change perceptibly 

 from day to day, in order to eliminate the effect of annual variation, 

 the differences between the abnormal variations of temperature at like 

 hours of consecutive days have been employed instead of the differ- 

 ences between the observed values, which, for the other elements, have 

 been considered sufficient. 



In seeking to establish the connection between the change in the 

 condition of an element and the wind that accompanies it, the change 

 has been referred to the resultant direction during the interval. When 

 the direction has not varied greatly during the day, this method may 

 be regarded as sufficiently accurate for the purpose designed ; but if 

 there be any very great change of direction, the resultant, though 

 geometrically equivalent to the actual winds as they reach the 

 anemometer, will not be necessarily equivalent in physical proper- 

 ties ; and if the resultant wind be from a direction for which the whole 

 number of resultants are few, errors will be introduced sufficient to 

 conceal the true character of that particular wind in its relation to the 

 element under consideration ; and hence conclusions relative to the 

 comparatively rare resultants, cannot be accepted for single months, 

 unless the errors be rendered inappreciable by extending the series. 



The tables in this article are derived from two series of observations 

 — one from 1S54 to 1859 inclusive, (two of the tables embrace also 

 the year 1853,) and the other from 1860 to 1862. Those that relate 

 to the pressure of dry air, the pressure of vapour, and the, relative 

 humidity are limited to the latter series ; but the tables for the tempera- 

 ture and the barometer have been computed separately for both series. 



The mean monthly and annual changes between the temperatures 

 and the barometric pressures at like hours on consecutive days were 

 computed in the first instance for the interval between 2 p.m. and 

 2 P.M. in the earlier series. Subsequently, when it was desired to 

 connect the diurnal change with the daily resultant direction of the 

 wind, since the resultants had been all calculated for the twenty-four 

 hours, commencing at G a.m., it became requisite to take the differ- 

 ences also for that same interval. The arrangement found most 

 convenient for collecting these differences, while it readily afforded the 



