of Edinburgh, Session 1880-81. 
305 
§ 13. We may now proceed briefly to discuss these in order, not 
tracing them into more detail than is essential for clearness. 
A. (1.) Of the extreme limits of time either or both may or may 
not be known, but the time at which our record of facts is taken can 
be, and usually is, stated definitely at the outset as a date. 
(2.) Limits of space. Leaving all purely physiographical ques- 
tions to the preliminary science of geology, the essentially social 
space relations may be arranged as follows : — 
A. Territory of given society. 
I. Quantity at given time. 
1. Persistent since last unit time. 
2. Added since last unit time. 
(a) By geologic agency (upheaval, deposition, &c.). 
(b) By social agency (discovery, conquest, reclamation, 
purchase, &c.). 
II. Quality at given time. 
1. Unused. 
2. Used. 
(a) Unspecialised (for such and such functions). 
(b) Specialised (for such and such functions). 
III. Decrease since last unit time. 
1. By geologic agency. 
2. By social agency. 
§ 14. Let us now pass to the body of facts which our third 
axiom enables us to co-ordinate — those (B) relating to the matter 
and energy utilised by the given society. 
The primary sources of energy in nature, so far as we at pre- 
sent know, are four — first, the primitive chemical affinity of the un- 
combined elements ; secondly, the internal heat of the earth ; 
thirdly, the rotation of the earth; fourthly, the sun. Of these 
the last is, of course, by far the most important ; and its energy 
exists either active in sunshine, moving air, or water, or latent in 
the earth’s crust, or in the organisms surrounding or composing 
society. The energy of the earth’s rotation has been used to some 
small extent in tide-mills ; that of the earth’s internal heat, as mani- 
fested in hot springs, volcanoes, &c., of course still less ; while the 
