264 Transactions of the South African Philosophical Socicty. 
forthcoming, and for the simple reason that they never existed. 
Good observations at Bloemfontein, and at Port Nolloth, and plenty 
of them, would be invaluable in the framing of a pressure theory for 
the table-land. Still more so would be a set of good records from a 
chain of stations across the continent near S. Lat. 29°. 
Failing such, as an experiment the monthly barometer results for 
Aliwal North, Philippolis, and Umtata, from the annual reports of 
the Cape Meteorological Commission have been compared with the 
observations for the same years at Durban.* They are each derived 
from one observation per diem, at VIII., of a marine barometer, the 
sluggishness of which may flatten the curves somewhat. 
Umtata, below the high table-land, shows the normal winter 
maximum difference, and summer minimum, with very little retarda- 
tion. Philippolis and Aliwal North both incline to Kimberley 
characteristics. The monthly rate of increase of mean pressure is 
pretty much the same for each station, i.e., the pressure curve for 
each is to all intents and purposes an inverted curve of table-land 
temperatures. [See Tables 39 and 40.] 
We may, it seems, without unduly magnifying the force of the 
evidence, regard the lagging in the differences of mean pressure as a 
peculiarity differentiating a table-land from a mountain in a germane 
latitude. The actual process seems to be much in this way :— 
1. The annual mean temperature of the air immediately over the 
table-land being much greater than that of the free air over the coast 
at the same elevation, the layers of equal pressure that would other- 
wise be level planes are expanded upwards in surfaces that follow the 
contour ofthe land. Those portions of the surfaces protruding thus 
above the elevation proper to their given pressures push outwards 
against the normal surfaces over the coast—not sliding upon each 
other as von Siemens has truly said +—until equilibrium is estab- 
lished. That is, for any given latitude the barometer would read 
lower on the table-land and higher on the coast than it would if the 
table-land were replaced by a mountain of the same altitude, because 
of this outward extension. 
* Some Durban results for VIII., Royal Observatory mean time, are published by 
the Cape Meteorological Commission each year; but they do not tally with those 
published direct by the Natal Observatory, and so have not been used here. It 
seems probable that before being sent to Cape Town they are corrected for latitude. 
If so, they are not really comparable with the results from the other coast ports 
published on one page as ‘‘ Monthly Means of Barometer . . . reduced to 32° F. 
and Sea-level,” none (or few at any rate) of which have undergone the latitude 
correction. 
+ “On the General System of Winds of the Earth” (Phil. Mag., 1890). But it is 
largely a question of words, although, perhaps, not quite true in the sense in which 
von Siemens intended. 
