l2 7 
Nov. i, 1885.] Tile Australasian Scientific Magazine. 
satisfactorily explained by philosophers, instead of travelling on the surface 
all the way from the pole to the equator, travels in the upper regions of 
the atmosphere until it gets near the parallel of 30 deg.” Here this upp.r 
current meets with an opposing current from the equator, and by their 
pressing against each other a calm and an accumulation ot the atmosphere 
is produced. In this calm region the barometer stands higher than it does 
either to the north or to the south of it, which is a proof of the banking up 
of the atmosphere in this latitude. “We can understand,” he says, “ why 
there should be an uprising of the air which the two systems of trade winds 
pour into the equatorial calms. But when this air commences to flow 
towards the poles as an upper current, we cannot understand why it should 
not continue gradually to descend and turn back all the way from the 
equator to the poles, nor, as far as investigation has gone, has any explana- 
tion been suggested for the calm belts of the tropics ; nor can we tell why 
the upper currents should meet at one parallel in preference to another. 
But the fact of a meeting and a preference is certain.” 
What we require then is a theory which will explain the westward ten- 
dency of both winds and currents in tropical regions, and at the same time 
show sufficient cause why an upper instead of a surface current of air 
moves from either pole to the tropics producing the calm belts of Cancer 
and Capricorn. If it can be shown that each of these phenomena is attri- 
butable to the same cause the theory will be a complete one, and it will be 
what correct theories always are, viz., simple and easy of application. It 
is somewhat strange that no attempt has been made hitherto to suggest a 
cause. Unfortunately, Halley’s theory has been adopted, without suffici- 
cient grounds, by nearly every subsequent writer, and therefore, instead of 
looking fora different cause, vain attempts have only been made to recon- 
cile or adapt his theory to the other unexplained phenomena. Let us, 
however, for a moment enquire how far heat and axial rotation in tropical 
regions does account for the existence of the north-east and south-east 
trade winds. No one will be found to question the fact that the sun’s 
heat is the cause of the trade winds moving towards the equator, and that 
if the earth were at rest these winds would blow from north to south in the 
northern hemisphere, and from south to north in the southern hemisphere. 
But does axial rotation in these latitudes impart to them their westward 
tendency. Of course, it must do this in some degree, but is it sufficient 
for the purpose ? A very simple calculation will show whether such is the 
case. Take the north-east trade for example. Uninfluenced by diurnal 
rotation it would move along the meridian say at the rate of twenty (20) 
geographical miles per hour, making an angle of 90 deg. with the equator. 
The angle actually made by this wind with the equator on an average in 
the Atlantic Ocean is 23 deg. Supposing this wind to start from latitude 
30 deg., which is its extreme limit, in three (3) hours it would reach the 
parallel of 29 deg., travelling along the meridian at the assumed rate. In 
order to cut this parallel at an angle of 23 deg. instead of 90 deg., how far 
must the earth have slipped from under it towards the east ? In other 
words, how much should the velocity of rotation have increased in passing 
from 30 deg. to 29 deg. north latitude? Without going minutely into the 
calculation, but just taking a rough estimate, it will be admitted that the 
increase should amount to at least 120 miles, or 40 miles per hour. Now 
the actual increase does not exceed 6 miles per hour in this latitude, and it 
rapidly diminishes for each degree to almost nil as we approach the equator. 
Therefore, as the result of axial rotation only, the equatorial winds 
