May 8, 1902] 
duces the most important effects, for the author regards 
it as only a part of a great series of disturbances which 
modified the earth’s crust as far away as the American 
continent. These are mainly responsible for the Glacial 
epoch, and the advance or retreat of the ice and the | 
variations in sea-level must be attributed to earth- 
movements during it. Often, he insists, the sea, rather 
than the land, has altered its level, owing to changes in 
the form of the ocean basins. No doubt this is true, 
but we think the author presses it too far. He has also 
such faith in land-ice as to introduce the Scandinavian 
ice-sheet to the Shetland Isles, without caring to explain 
how it got across the deep valley which contours the 
southern and western coast of Norway. The earth- 
movements already mentioned were sometimes rapid, 
and the author connects the later of them with traditional 
deluges. The fabled Atlantis is Brazil, which had been 
converted into an insular tract by a rise of the sea. All 
this is certainly ingenious, though it may be unconvinc- 
ing. Healso gives us an explanation of the curious “ bone 
beds” of Pikermi. Downward movements (connected 
with the second set of faults) submerged the lowlands. 
The animals fled for refuge to the hills, where they were 
killed e2 masse by mephitic vapours, which, fortunately 
for geologists, were exhaled in the nick of time, and 
their dead bodies were afterwards carried lower down by 
floods and mudstreams. Cvredat Jude@us ! 
Last Words on Materialism. By L. Buchner. | Trans- 
lated by J. McCabe. Pp. xxxiv + 299. (London: 
Watts and Co., Igor.) Price 6s. net. 
IT can scarcely have been the intrinsic worth of these 
occasional essays which induced the “ Rationalist Press 
Association” to circulate them in an English dress. The 
volume is marked by all the confident dogmatism and 
loose reasoning for which the author of ‘Force and 
Matter” is unfavourably known to serious students. Its 
value as a contribution to genuine thought on the ulti- 
mate constitution of the world around is of the slightest. 
The authors position is that thought and will are 
secondary derivatives of a reality which is, in its own 
nature, “ material” in the sense of being not mental, but 
for this position no proof whatever is offered. The 
“idealist,” who comes in for a good deal of abuse which, 
from an English point of view, must be pronounced de- 
cidedly undignified, is never fairly met. His real argu- 
ment, that the physical world itself is only given us in 
terms of the experiences of a sentient perceiver, is 
quietly ignored, and he is only allowed to make the | 
futile objection that he does not know by what special 
process physical energy is “ transformed” into conscious- 
ness. The writer’s competence in philosophic discussion 
is shown by the fact that he thinks the inability of 
savages to count beyond four a proof that mathematical 
science is purely empirical. 
view of the presence of an a@ f7zorz element in knowledge 
refuted by the irrelevant appeal to the fact that know- 
ledge has been acquired by a process of gradual develop- 
ment. The real point has, of course, nothing to do with 
the process by which we come to know;; it is purely a 
question of how knowledge is constituted when you have 
got it. 
such essays as those on “ Hobbes” and on “ Buddhism 
and Christianity” are even sorrier stuff than the rest of | 
the book. Biichner seems to have known little or nothing 
about the subject ; he repeats complacently the absurd 
farrago by which Pythagoras has been brought into con- 
nection with Buddha, and expressly praises Hobbes for | 
The | 
being—precisely what he was not—an empiricist. 
“ Rationalist Press Association” is doing scientific thought 
no good service in issuing such a mixture of anti- 
ecclesiastical rhetoric and crass metaphysical dogmatism 
as representing the views of serious science about the 
world iho la Ibs 
NO. 1697, VOL. 66 | 
Similarly, he thinks Kant’s | 
The excursions into philosophic history made in | 
NATURE 
i 
29 
LETIERS TCO THE EDIROR: 
(The Editor does not hold himseif responsible for opinions ex- 
pressed by hts correspondents. Neither can he undertake 
zo return, or to correspond with the writers of, rejeced 
manuscripts intended for this or any other part of NATURE, 
No notice ¢s taken of anonymous communications.) 
The Misuse of Coal, 
WHILE most thoroughly agreeing with Prof. Perry in his 
desire to see a more efficient use made of our coal-supply, I yet 
think that he has drawn far too gloomy a picture of the future, 
and I wish to draw attention to a consideration which does 
not seem to have been present in his mind, or to have occurred 
to any of those hitherto dealing with the question as either 
authors or inventors. Prof. Perry says that ‘‘ scientific men 
know of no other store of energy available for man’s use than 
fuel from the earth, except what we may get by the help of the 
tides or by the wind or waterfalls.” With the exception of the 
tides, the energy of all these sources is derived ultimately, as is 
also that of coal itself, from the heat radiated by the sun, and 
what I wish to point out is that the heat of the sun may be 
made to furnish power in quite another way—a way, in fact, 
indicated by Nature herself. 
Prof. Perry points to animal organisms as types of efficient 
engines. Now, what is the fuel consumed by these engines? 
Obviously it is vegetable matter which derives its energy from 
the solar radiation of the present day. At the same time, it is 
evident that at the present moment only a small percentage of 
the solar radiation falling on the surface of the earth is used in 
this way; yet it will be found that the amount of energy 
derived from this source is very large compared with that pro- 
vided by our coal-supply. The detailed calculation cannot be 
attempted here, but a few figures will serve to show the order 
of magnitude we are dealing with. Taking Prof. Perry’s figure 
for a year’s coal-consumption at 663 million tons, and taking the 
average efficiency of engines at 3 lb. of coal per horse-power hour 
—whichis probably too high an efficiency—the figures work out 
to an annual output of 495,000 million horse-power hours, and 
this is roughly equivalent to 56 million horse-power working 
continuously night and day. Considering the number of human 
beings, horses, cattle and sheep, and considering their output 
in heat as well as in mechanical work, it is evident that the 
energy supplied by food—however efficiently used—must be 
vastly greater than that given by our present coal-consumption. 
Here, then, is an enormous source of energy only partially 
tapped at present—the heat radiated to the earth by the sun— 
and the method of using it is indicated by Nature. When our 
stock of fuel approaches exhaustion, we shall—so it appears to 
me—have to set to work and—to put it crudely—grow our own 
fuel as we go along. 
The use of vegetable matter for fuel is by no means unknown 
even to-day; for although wood has long ceased to compete 
with coal as a fuel, yet in Germany at the present time a new 
industry is growing up in the production of crude spirit from 
potatoes. This spirit is used as a cheap fuel in internal-com- 
bustion motors, and is therefore evidently able to compete with 
earth-fuels even in a northern country where solar radiation is 
not very intense and land-values are high. The progress from 
the use of wood and charcoal as a fuel to the use of potato- 
spirit is so great that we may reasonably expect much more in 
the same direction when once attention has been concentrated 
upon the matter. In fact, it may not be too much to expect 
that ultimately the regeneration of carbon from the dioxide of 
the atmosphere may be accomplished by means of synthetically 
prepared bodies which—somewhat like the chlorophyll of the 
living plant—are capable of decomposing carbon dioxide under 
the influence of sunlight. In those circumstances, the solar 
heat used in the evaporation essential to the growth of plants 
might be saved for the direct production of fuel, and the yield 
per acre of sunlit area greatly increased. I think, therefore; 
that in ‘* fuel farming,” in the first instance by the most prolific 
plants available, and ultimately by purely chemical agents, the 
problem of the supply of energy after the exhaustion of the 
world’s coal-supply may perhaps be solved. All I am here try- 
ing to show is that the quantity of energy available by these 
means is large compared with the power actually in use at the 
present day, and even this I have only indicated in the roughest 
way; but I agree with Prof. Perry as to the extreme import- 
ance of the question, and I think with him that it is a matter of 
vital national importance. If, however, fuel farming is really a 
