ON ATMOSPHERIC WAVES. 139 
the barometer first descending with the S.E. wind as the trough approaches 
stations to the N.E., and rising with the N.W. as the current produced by 
the rarefaction approaches, until the crest passes, when the new counter cur- 
rent or slope of the next wave would set in *. 
Pursuing this idea further, there can be no question that Ireland and 
Scotland become points, or unitedly constitute a great point of rarefaction, 
forming as they do the nearest land to the northern part of the Atlantic, the 
Jand becoming hotter than the neighbouring water, and in consequence a 
N.W. current with its compensating current from the S.E. is induced. Not 
only will the rapidity of the currents reduce the pressure, but the ascending 
column from the land will transfer some of the air into the general current 
of the atmosphere, and there will be a real difference in the distribution of 
air as well as pressure ; a section transverse to the line of greatest velocity 
will exhibit a hollow or trough, and the same phenomena will result from 
this arrangement of the aérial currents as we noticed arising from the N.E. 
and S.W. currents, the only difference being in direction. 
The following marine stations are admirably suited for testing the views 
just advanced, and tracing a wave of this system from the most western 
point of Africa to the north of Europe. 
Cape Verd. Lisbon. Glasgow. 
Cape Verd Islands. Oporto. Inverness. 
The Canaries and Madeiras. Corunna, The Western Isles. 
| The Azores as an outlying Brest. The Orkneys. 
! station. The Scilly Islands. |The Shetland Isles. 
_ Astation in Morocco near Cape Clear. Christiania. 
Cape Cantin. Limerick. Coast of Norway near 
Tangier. Galway. the Arctic Circle. 
Gibraltar. Markree. Hammerfest or Alten. 
Cadiz. 
A station in Iceland as an outlier would be very valuable. 
The following inland stations are calculated to exhibit the influence of the 
land in modifying the waves in their progress towards the N.E. 
St. Petersburg. « Prague. Venice. Naples. 
Warsaw. Vienna. Rome. Tunis. 
In thus considering these rectangularly posited systems of parallel and 
opposite currents, many complex anemonal and barometric phenomena re- 
ceive an easy explanation, particularly the revolution of the vane in one 
- uniform direction, and the barometric wind-rose. When the conterminous 
edges of any two currents pass a station, the barometer is either at a maxi- 
_ mum or minimum with respect to that particular system of currents; the 
_ wind also changes at this time. If the barometer has previously been rising 
_ with a north-easterly wind, it now begins to fall with a south-westerly : the 
cross currents are however passing at this time with a lateral motion towards 
_ the N.E.; in this set of cross currents the barometer will rise with a north- 
westerly wind and fall with asouth-easterly. Suppose while the posterior slope 
_ of a N.W. wave transits, wind S.W., and before its trough passes, the trough of 
the cross wave from the S.W. also transits, and is immediately succeeded by the 
_ following anterior slope with its N.W. current, the wind will pass from S.W. 
‘to W. Now while this slope continues, upon the trough of the N.W. system 
_ passing, the wind changes to N.E., and the resultant of the two currents is N. 
It is easy to pursue this reasoning, and thus trace the changes of the wind 
_ arising from these two cross systems completely round the compass. 
f - * Tn the above suggestion I have considered the northern portion of the African continent 
as inducing the N.W. current, but of course, the entire surface, as far as the extreme north of 
__ Europe, including Great Britain and Ireland, will act as a rarefying surface. 
