E.—GEOGRAPHY. . 99 
Be 
imagine life existing on Mercury or on Neptune ; liquids boil on the 
former and freeze hard on the latter. Millions of millions of stars 
exist which support no life. At the best, life must be limited to a tiny 
fraction of the Universe.’ 
In the face of such utterances I think that geographers should be rid 
of that inferiority complex which the historians on the one hand, and the 
_ geologists on the other, have too frequently managed to impose upon them. 
A planet with a hydrosphere is a@ unique object of study. This earth is 
important not merely subjectively and because we men who inhabit it 
‘are the students; in the university of the impartial angels it would be 
an object of intense interest and speculation. May we not compare it 
with radium among the elements? Just as radium, almost infinitesimal 
in quantity, has by its activity revealed the energy locked up in the 
commoner atoms, so may not the hydrosphere of our earth present the 
infinitesimally rare conditions under which life becomes active which 
elsewhere through the Universe is immanent, but potential and not 
active 2 
_ Three years ago, in an address to the International Geographical Con- 
gress at Cambridge, I described the hydrosphere in words which I will ask 
po leave to use again :— 
. the hydrosphere, a term invented to cover the totality of 
water on the earth whether gathered together in the ocean, or invisible 
in the air, or condensed in the clouds, or falling as rain or snow, or 
creeping down in the glaciers, or coursing down in the rivers, or 
percolating underground, or rising in the sap of plants or circulating 
in the arteries and veins of animals. There is probably no complete 
lacuna in the hydrosphere, though there are thin places over and in 
the deserts. It would be a vast bubble, if we imagine all else dis- 
solved away. Moreover, the hydrosphere is functionally one, for 
given sufficient time and every drop might successively take the place 
of every other drop, passing from the ocean back into the ocean. 
Obviously life, and not least human life, is possible only within the 
bounds of the hydrosphere. In purely physical geography nine- 
tenths of the processes investigated are dependent on the physical 
properties of water. It is a remarkable fact that within the short 
range of temperatures on the earth’s surface lies the whole gamut of 
_ the changes of state in water, with all the consequences which flow 
from a high specific heat and the liberation and absorption of great 
latent heats. The atmosphere exhibits climatic contrasts chiefly 
by reason of its contained moisture. Propelled by the sun’s energy 
from without, water is the chief sculptor of the solid forms upheaved 
_.by the earth’s energy from within. Without water there would be 
_ no agriculture, nor would coal and iron have been deposited for our 
mines. Even man must earn his living by the sweat of his brow.’ 
Let me hasten to add that in this advocacy of the claims of the hydro- 
sphere to be considered as the central theme of geography, I am not 
getiul of the just rights of the lithosphere, which has of late been 
nant in our geographical argument; nor yet do I forget the part 
ed by the winds and the oxygen of the atmosphere. We will, if you 
like, define the object of geographical study as extending to those parts 
H 2 
