of Edinburgh, Session 1*878—79. 
219 
be exemplified by S.W. winds, which cause a fall in the baro- 
meter, while N.E. winds create a rise. South-west are accompanied 
by rapid upper currents, and let these be represented in the diagram 
No. 5 by the arrow AB, while the less rapid currents beneath are 
exhibited by the shorter arrows. RS is the surface of the ground. 
A. ' B 
R S 
Diag. Bo. 5. 
Let the narrowing in the parallel position of the upper arrows repre- 
sent accumulation aloft, and their widening below represent rarefac- 
tion and diminution of pressure. In this way, and also owing to 
removal of air, the fall of the barometer with these winds may be 
shown. North-east winds are not accompanied by rapid upper cur- 
rents, which move somewhere about the same rate of speed as those 
on the surface. For the sake of illustration, let it be supposed that 
they move even more slowly, and let them be indicated by the shorter 
arrows AB above, while the more rapid surface currents passing over 
the surface RS are shown by the longer arrows beneath. In this case 
<5 A 
< 
< 
s * ' R 
Diag. No. 6. 
surface retardation, in so far as it is indicated by the difference 
betwixt the comparative speed of the currents below and above, 
will not here be found, although, of course, it really takes place. 
Accumulation aloft cannot here be found ; it will now take place on 
the surface, as is shown in this diagram by the closeness of the 
parallel position of the arrows there. This tendency to condensation, 
which was also to be found in the former instance, was there removed 
by the rapid upper currents, which here are not to be found. With 
these N.E. winds, therefore, as removing and lifting does not take 
