ALLISON — NOVA SCOTIAN METEOROLOGY. 303 



thermometer, are found the force of vapour and the relative 

 humidity corresponding to these temperatures." Let the apparent 

 height of the column, reduced to 32° and to sea-level, be 29.800 

 inches, the temperature of air 43°, and of the wet-bulb 40°, — the 

 difference thus being 3° ; then you will use the psychrometrical 

 table as above, and subtract 0.208 as force of vapour, giving the 

 result — 



29.800 inches. 

 — 0.208 " 



29.592 " 

 as pressure of dry air, and the relative humidity will be 75.0. 

 But suppose the barometer, and the difference between dry and wet 

 bulbs, to be still the same, but the wet to be fallen to 33°, then 

 you will subtract only 0.149, giving — 



29.800 inches. 

 — 0.149 " 



29.651 " 

 as dry pressure, and a relative humidity of 70.5. This will 

 readily explain how necessary it is to take into account the tem- 

 perature and difference of the bulbs, when calculating climato- 

 logical results from barometric observations. The difference is 

 increased or diminished simply by evaporation, depending again 

 upon.the capability of the atmosphere to hold moisture. Even in 

 the heaviest rains there is generally a degree or more of difference 

 between the thermometers ; but a fog is complete saturation, or 100 

 per cent, of relative humidity. 



As Nova Scotia has a less pressure than corresponds to its 

 latitude, so should it have a greater heat than its proper due ; but 

 the immense stretches of snow and ice prevent that during the 

 longer portion of the year ; and as these frozen regions of land 

 and water lie from the north-west to the north-east of us, and exert 

 their influence over us from November to June, we have less heat 

 during that period than might otherwise be expected. The mean 

 yearly temperature of Halifax is 42°. 81 ; of Digby, 43°. 50; of 



