370 ACCOUNT OF THE ATICTIC REGIONS. 



the greatest heat 93°.5 ; the mean is 48°. 75 or 

 1°.65 less than the mean temperature of the 

 same period. Even the mean of the extremes 

 of temperature observed in any one year, does 

 not differ so considerably from the mean of 

 the year as might be imagined. One year, in- 

 deed, in London, the mean of the yearly ex- 

 tremes was 8°.l below that of the mean tem- 

 perature ; but in the 20 years, the mean of 

 the extremes corresponded with that of the year, 

 4 times to within a degree, 10 times to 

 within 2°, 12 times to within 3°, 15 times to 

 within 4°, 17 times to within 5°, and 19 times 

 to within 6°. Hence it is as great a probabi- 

 lity that the mean of the yearly extremes of 

 temperature is within 2° of the mean tempe- 

 rature of the same year, as that it differs more> 



SECT. III. 



Remarks on the Pressure of the Atmosphe?T^ 

 with Observations on the Use of the Barome- 

 ter in predicting the Weather. 



In the winter and spring months, the pressure of 

 the atmosphere, in polar latitudes, as well as its 

 temperature, is liable to sudden and very consider- 

 able variations. But as my observations have been 



2 



