of Edinburgh, Session 1868-69. 
465 
2. Note on the Determination of Heights, chiefly in the 
Interior of Continents, from Observations of Atmospheric 
Pressure. By Alexander Buchan, M.A., Secretary of the 
Scottish Meteorological Society. 
The weight or pressure of the atmosphere is ascertained by the 
mercurial barometer, the aneroid, or from the temperature of the 
boiling point of water. The height of a hill is measured baro- 
metrically, from observations made simultaneously at its base and 
top, and the application of certain well-known formulas. The 
height of a place at no great distance from another place whose 
height is known, and at which observations are made about the 
same time, may similarly be ascertained with a close approximation 
to the truth. 
But, with regard to places far from any place of known elevation, 
or from any place at which meteorological observations are made, 
it is plain that the height can only be computed by assuming a 
certain pressure as the sea-level pressure at that place. 
In the Table giving the reductions of heights from Captain 
Speke’s observations, it is stated (Journal of the Royal Geographical 
Society, vol. xxxiii.) that a mean pressure of 29'92 inches was 
assumed as the mean sea-level pressure, — that is, if those parts of 
Africa visited by Speke had been on the same level with the sea, 
it is assumed that the mean pressure of the atmosphere would have 
been 29 ’92 inches. 
In the last revised “ Hints to Travellers,” prepared by the Royal 
Greographical Society, and published in the Journal, vol. xxxiv., it 
is stated at page 286, “ When the boiling point at the upper 
station alone is observed, we may assume 30*00 inches, or a little 
less, as the average height of the barometer at the level of the sea. 
The altitude of the upper station is then at once approximately 
obtained from the tables.” So far as I have been able to ascertain, 
this mean height of the barometer has been generally accepted by 
travellers as applicable to all seasons, and to all parts of the globe at 
great distances from Meteorological Observatories. Unfortunately, it 
has hitherto been generally the practice for travellers, or those who 
have been intrusted with reducing their observations, to give only 
the heights deduced from the observations, with a curious minute- 
