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of Edinburgh, Session 1878 - 79 . 
found, and where barometric observations are not always absolutely 
reliable, nor also are the gradients and isobars which depend upon 
them. In such an imperfect state of matters, exceptional cases must 
always be found, and these, if not disadvantageously too numerous, 
must consequently, as above remarked, be regarded as being a 
negative test or proof of the conclusions arrived at. The import- 
ance of barometric observations is however well known, but, as has 
been pointed out by the Astronomer Royal and others, a great mass 
of these is valueless and simply overwhelming, while comparatively 
few definite conclusions have as yet been arrived at. Hence ex- 
planatory theories must be produced to point out the particular 
direction in which such observations ought to be carried out. In 
such a subject as this, the greater the extent to which investigation 
takes place the greater will be the amount of difficulty and com- 
plexity, but such a discovery is only to be regarded as being a more 
accurate approach to ultimate reliable conclusions. 
The object of this paper is to show, mainly in a mechanical point 
of view, why the fall of the barometer to a great extent is due to 
strong winds, setting aside at present the much smaller amount of 
fall produced by heat and vapour. In other words the point to be 
explained is, — why horizontal movement takes off vertical pressure. 
This fall, due to strong winds, is produced by a real removal of air 
and the amount to which it takes place will depend on the extent 
of the resisting surface over which the winds pass, and also on the 
amount of their source of supply, which is indicated so far by the 
steepness of the gradients. In a somewhat similar way, when the 
incline at the bottom of a river is very slight, the current will then 
move slowly, and will tend to deepen and accumulate, but when the 
incline is much steepened, the current will then increase in speed, 
removal will now take place, and it will consequently shallow out. 
Although the barometer thus falls for “ removal” of air, it is intended 
to show that this fall is not entirely due to removal, but that it is 
also partly due to “lifting,” which is an exhibition of fictitious pres- 
sure. The barometer has been described as being both a cause and 
an effect. An area of low pressure is a cause of the indraught of 
aerial currents, but owing to the peculiar mode in which they inflow 
to this low centre by rapid upper currents, a still further diminu- 
tion of pressure will take place, as just above mentioned, and this 
