854 W. Ferrel—Relation between the Barometric Gradient 
sons. This we know is the case in the southern hemisphere, 
where the most southern observations, obtained mostly by 
the British Board of Trade, were neces sarily made during the 
summer season, when the barometric pressure is the greatest 
in those latitudes. If, however, it can be clearly shown by 
observation that the mean annual a egg is a minimum at 
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real he bin ae and directions of the mean constant 
winds aos, been determined only very roughly from observa- 
tion on any part of the slebé and. hence no cagh accurate com- 
parisons of our law with observation can be made. Such com- 
parisons, however, all seem to establish the trath of the law 
within the limits of the errors of observation. The mean ed 
stant isobars in the British Islands, as determined by 
Glaisher, all effects of the seasons and of local disturbing causes 
eing eliminated, gives very nearly G=0-02 of an inch. 
= value in (1), supposing the direction of the wind to oF 
e east, or nearly so, or that the value of ¢ is small, we 
noe v=6 se nearly. This is a very little less than the mean 
eastward velocity of the wind here, as determined by the late 
is — anc given in his “ Winds of the Northern Hem- 
the usual velocity of the trade winds, so that the result seems 
to confirm our law with regard to velocities. 
From the table of barometric pressures given by Buchan, 
hich has been already referred to, we obtain for the parallel 
