THE 
VOYAGE OF H.M.S. CHALLENGER. 
PHYSICS AlYD CHEMISTRY. 
REPORT on Oceanic Circulation, based on the Observations made on 
board H.M.S. Challenger, and other Observations. By Alexander 
Buchan, M.A., LL.D., F.R.S.E. 
During the two or three years preceding the time when the Challenger left on her 
famous voyage, several large questions, both practical and scientific, affecting the general 
movements of the atmosphere and the ocean began to be discussed, with an intelligence 
and fulness new to the discussion of such questions. These discussions were 
occasioned by the correct deep-sea temperatures which then began to be obtained, 
and by a first approximate representation of the distribution over the earth of the mass 
of the earth’s atmosphere, thus leading to a more accurate knowledge of the prevailing 
winds of the globe resulting from that distribution. At that time, any discussions that 
were attempted on the more fundamental problems of meteorology, relative to the 
diurnal and seasonal changes in atmospheric temperature, pressure, humidity, and wind, 
were really restricted to observations made on land. It was plain that data obtained 
exclusively from observations made on laud, which occupies little more than a fourth 
part of the earth’s surface, were inadequate to a right conception and explanation of 
atmospheric phenomena. 
Accordingly, when the Challenger Expedition was fitted out in 1872, arrangements 
were made for taking, during the cruise, either hourly or two-hourly observations both 
of atmospheric phenomena and of the surface temperature of the sea ; and in addition, 
elaborate observations of sea temperatures and specific gravities of the sea- water at all 
depths. Immediately on publication in the Preliminary Reports of the Expedition, 
the results of these observations were at once recognised to be of first importance in 
terrestrial physics, inasmuch as they opened up for discussion the broad question of 
oceanic circulation on a basis of accurate facts. 
It became more and more evident, as the examination of the results was proceeded 
with, that, for a right understanding of the questions raised, a full discussion of 
atmospheric phenomena was required as a necessary preliminary. Now, of these 
(PHYS. CHEM. CHALL. EXP. PART VIII. 1895 .) 1 
