MAGAZINE OP SCIENCE AND ART. 
209 
ture of the place must exceed 70°_Fahr.; and on the 
other hand, the vine cannot be cultivated successfully 
when the temperature is 72 w or upwards. Hence, the 
mean temporature of any place at which these two 
plants flourished and bore fruit must lie between these 
narrow limits, i e. could not difter from 71 c Fa.hr. by 
more than a singlo degree. Now, from the Bible wo 
learn that both plants were simultaneously cultivated 
in the central valleys of Palestine in the time of Moses, 
and its then temperature is thus definitively deter¬ 
mined. It is the same at the present time ; so that the 
mean temperature of this portion of the globe has not 
sensibly altered in the course or thirty-three centu¬ 
ries. . . 
The future of physical sciences seems to lie in the 
path upon which three of our ablest British physi¬ 
cists have so boldly entered, and in which they have 
already made snch large advances. I may therefore 
be permitted briefly to touch upon the successive stops 
in this lofty generalization, and to indicate the goal to 
which they tend. It has been long known that many 
of the forces of nature are related. Thus, heat is pro¬ 
duced by mechanical action, when that is applied in 
bringing"the atoms of bodies neater by compression, or 
when it"is expended by friction. Heat is developed, by 
electricity, when the free passage of the latter is im¬ 
peded ; it is produced whenever light is absorbed; and 
it is generated by chemical action, A like interchange¬ 
ability probably exists among all the other forces of 
nature, although in many the relations have not been 
so long perceived. Thus, the development of electricity 
from chemical action dates from the observations of 
Galvani; and tho production of magnetism by elect¬ 
ricity from the discovery of Oersted. The next great 
step*was to perceive that the relation of the physical 
forces was mutual; and that of any two, compared, 
together, either may stand to tho other in relation of 
cause, "With, respect to heat and mechanical force, this 
hasten long known. When a body is compressed by 
mechanical force, it gives out heal ; and, on the other 
hand, when it is healed , it dilates and evolves. power. 
The knowledge of the action of electricity in .dissolving 
the bonds of chemical union followed closely upon 
that of the inverse phenomenon ; and the discovery of 
clectro^magnetism bv Oersted was soon followed by 
that of magneto-eleciricity by Faraday. With reason, 
therefore, it occurred to many minds that the relations 
of any two of the forces of nature wqro mutual — 
that which is the cause , in one mode of interaction, 
may become the effect when the ordei 4 of the pheno¬ 
mena is changed; and that, therefore, in the words 
of Mr. Grove, one of the able expounders of these 
views, while they are “corelative,” or reciprocally 
dependent, “neither, taken abstractedly, can be said 
to be the essential cause of the others But, a 
further step remained to be taken. If these forces 
•were not only related, but mutually related, was it not 
probable that the relation was also a definite one? 
Thus, when heat is developed by mechanical action, 
ought we not to expect a certain definite proportion to 
subsist between the interacting force, so that if 
one were doubled or trebled in amount, the other should 
undergo a proportionate change. This anticipation, it 
has been already stated, has been realised by Mayer 
and Joule. The discovery of the mechanical equiva¬ 
lent of heat has been rapidly followed by that of other 
forces;and we now know not only that electricity,mag¬ 
netism, and chemical action, in given quantities, will 
produce each a definite amount of mechanical work, 
but we know further—chiefly through the labours of 
Mr. Joule—what that relation is, or in other words, the 
mechanical equivalent of each force. The first step in 
this important career of discovery—though long un¬ 
perceived in its relation to the rest—was, undoubtedly, 
Farraday’s great discovery of the definite chemical 
effect of the voltaic current. Tho last will probably 
be to reduce all these phenomena to modes of motion, 
and to apply to them the known principles of dyna¬ 
mics, in such a way as not only to express the laws of 
each kind of movement, as it is in itself, bnt also the 
connection and dependance of tho different classes of 
the phenomena. 
A bold attempt at such a generalization has been 
made by M. Helmholtz. The science of Thermo¬ 
dynamics starts from the principle, that perpetual 
motion is impossible, or, in other words, that we cannot, 
by any combination of natural bodies, produce force out 
of nothing. In mechanical force, this principle is 
reducible "to tho known law of tho conservation of vis 
viva ; and M. Helmholtz has accordingly endeavoured 
to show that this law 7 is maintained in the interaction of 
all the natural forces; while, at the same time, tlio 
assumption of its truth leads to some new consequences 
in physics, not yet experimentally confirmed. Ex¬ 
pressed in its mos*t general form, this principle asserts 
that the gain of vis viva during the motion of a system, 
is equal to the force consumed in producing it; from 
which it follows, that the sum of the vires Viwe, and of 
the existing forces, is constant. This principle M. 
Helmholtz denominates the conservation of force , A 
very important consequence of its establishment must 
be, that all the actions of nature are due to attractive 
and repulsive forces, whose intensity is a function of 
the distance—the conservation of vis viva holding only 
for such forces. It is usually stated, in mechanical 
works, that there is a loss of vis viva in the_ collision of 
inelastic bodies and in friction. This is true with 
respect to the motion of masses, which forms the sub¬ 
ject of mechanical science at present limited; but it is 
not true in a larger souse. In these, and such-like cases, 
the movement of masses is transformed into molecular 
motion, and thus reappears as heat, electricity, and 
chemical action; and the amount of the transformed 
action definitely corresponds to tho mechanical force 
which w r as apparently lost. In the cases just considered, 
mechanical action is converted into molecular. But 
molecnlar actions of different kinds are themselves in 
like manner interchangeable. Thus, when light is 
absorbed, vis viva is apparently last; but—not to speak 
of phosphorescence, in which the light absorbed, or a por¬ 
tion of it, is again given out—in all such cases, heat and 
chemical action are developed, and in amount corres¬ 
ponding to the loss. Hence the apparent exceptions 
to the principle are in reality confirmations of it; and 
we learn that the quantity of force in nature is as 
unchangeable as the quantity of matter. This, however, 
is not true of the quantity of available force . It follows 
from Carnot’s law that heat can be converted into 
mechanical work only when it passes from a warmer to 
a colder body. But the radiation and conduction by 
which this is effected tend to bring about an equilibrium 
of temperature , and therefore to annihilate mechanical 
force: and the same destruction of energy is going forward 
in the other processes of nature. Thus it follows from 
the law of Carnot, as Prof. Thompson has shown, 
that the universe tends to a state of eternal rest; and 
that its store of available force must be at length 
exhausted. Mr. Kankine has attempted, in another 
method, to combine the physical sciences into one system, 
by distinguishing tho properties which the various 
classes of physical phenomena possess in common, and 
by taking for axioms propositions which comprehend 
their laws. The winciples thus obtained are applicable 
to all physical change; and they possess all the 
certainty of the facts from which they aro derived by 
induction. The subject-matter of the science so consti¬ 
tuted is energy » or the capacity to effect changes; and 
its fundamental principles are, first, that all kinds of 
energy and work are homogeneous—or, in other words, 
that any kind of energy may be made the means of 
performing any kind of work ; and, secondly, that tho 
total energy of a substance cannot be altered by the 
mutual action of its parts. From these principles the 
author lias deduced somo very general laws of the 
transformation of energy , which include the known 
relations of physical forces. 
I have occupied your time so largely with the sciences 
of one Section, that I cannot do more than advert to one 
