6 
sioned by friction of the tidal waves, as well 
as by their forming, as it were, a drag upon the 
earth’s rotatory movement, the velocity of the 
earth’s rotation must be gradually dimi- 
nishing, and that thus unless some 
undiscovered compensatory action exist, 
its rotation must ultimately cease, and 
changes hardly calculable take place 
in the solar system. He adds, that M. Delau- 
nay considers that part of the acceleration of 
the moon’s mean motion, which is not at pre- 
sent accounted for by planetary disturbances, 
to be due to the gradual retardation of the 
earth’s rotation ; to which view, after an 
elaborate investigation, the Astronomer Royal 
has given his assent. There are some diffi- 
culties, not perhaps insuperable, in another 
speculation of Mayer, viz., that the heat of the 
sun is occasioned by friction or percussion of 
meteorites falling upon it. Then, after point- 
ing out that, enquiry may arise as to what 
becomes of the light and heat radiated into 
space, the President passes on to molecular 
physics, in which field the doctrine of correla- 
tion of forces is steadily making its way. In a 
practical point of view, the power of converting 
one mode of force into another is of the highest 
importance; and with reference to a subject 
which at present — prematurely, perhaps — 
occupies men’s minds, viz,, the prospective 
exhaustion of the coal-fields of England, 
there is every encouragement derivable from 
the knowledge, that we can at will produce 
heat by the expenditure of other forces-; but, 
more than that, we may probably be able to 
absorb or store up, as it were, diffused 
energy. The example of formate of potash, 
and others similar, may calm apprehension as 
to future means of supplying heat, should our 
present fuel become exhausted. As the sun’s 
force, spent in times long past, is now returned 
to us from the coal which was formed from 
that light and heat, so the sun’s rajs, which 
are daily wasted, as far as we are concerned, 
on the sandy deserts of Africa, may hereafter, 
by chemical or mechanical means, be made to 
light and warm the habitations of the denizens 
of colder regions. The tidal wave is, again, a 
large reservoir of force hitherto almost unused. 
The researches of Tyndall afford instances of 
localising, if the term be permitted, heat which 
would otherwise be dissipated ; and those of 
Graham afford indications of means of storing 
up force. We are at present far from seeing a 
practical mode of replacing those granaries of 
force — coal-fields ; but we may with confidence 
rely on invention being in this case, as iu 
others, born of necessity, when the necessity 
arises. There hardly seems a limit to the 
extent to which mechanical may be con- 
verted into electrical force. As we may, in 
a not very distant future, need, for the daily 
uses of mankind, heat, light, and mechanical 
force, and find our present resources ex- 
hausted, the more we can invent new 
modes of conversion of forces, the more pro- 
spect we have of practically supplying such 
want. Mr. Grove then passes on to physiology, 
in which considerable strides are being made 
by studying the relation of organized hodies 
to external forces. Vegetables, acted on by 
light and heat, produce certain chemical 
changes. The animal reverses the process ; but 
it must not be forgotten that the line of demar- 
cation between a vegetable and an animal is 
difficult to draw, — that there are no single 
attributes which are peculiar to either— -and 
that it is only by a number of characteristics 
that either can be defined. That musular 
action is produced or supported by chemical 
change would probably now be a generally- 
accepted doctrine ; but recent researches seem 
to show that the oxidation of albuminous or 
nitrogenized substances is rather an accompani- 
ment than a cause of muscular force, and that 
it is by the oxidation of carbon and hydrogen 
that such force is supplied. We must not 
confuse the question of the food which gives 
permanent capability of muscular force, with 
that which supplies its requisites of temporary 
activity. Some of the graminivora have 
great capacity for temporary exertion, 
but for concentrated and sustained 
energy they do not equal the carni- 
vora. And the domestic graminivora are 
capable of performing more work when sup- 
plied with those vegetables which contain the 
greatest quantity of nitrogen. Mr. Grove be- 
lieves the day is approaching when inventions 
of entities made to vary according to the re- 
quirements of the theorist will be dispensed 
with, and when the two fundamental concep- 
tions of matter and motion will be found suf- 
ficient to explain physical phenomena. He 
considers that geology affords striking evidence 
of continuity, and that the breaks iu the record 
do not represent sudden changes in the forma- 
tion of the earth’s crust, but rather arise from 
dislocations occasioned since the original depo- 
sition of strata, or from gradual shifting of the 
areas of submergence. Then comes the ques- 
tion whether, when the geological formation is 
continuous, the different characters of the 
fossils represent absolutely permanent varieties, 
or may be explained by gradual modifying 
changes. The physical breaks in the stratifica- 
tion make it next to impossible to fairly trace 
the order of succession of organisms by the 
evidence afforded by their fossil remains, but 
many geologists seem to believe that the 
succession of species bears some rela- 
tion to the succession of strata. Indi- 
cations, too, of the connection between cosmical 
studies and geological researches are dawning 
on us, and Mr. Grove, like Sir J. Herschel, 
seems impressed with the magnificence of that 
view of geological revolutions which regards 
them rather as regular and necessary efforts of 
great and general causes, than as resulting from 
a series of convulsions and catastrophes 
