Dee. 1, 1870 | 
NAT 
URE 89 

there is any change, all changes must be most carefully 
shown in any manner the artist may prefer. 3. Espe- 
cially note alllong streamers. 4. All tints and change 
of tint, and whether the colour is distributed in patches 
or in layers concentric with the moon, or in connection 
with the prominences. 5. Whether it consists of a level 
patch of luminous haze or radiating beams of light, or of 
bundles of hyperbolic rays. 6. If of radiating or hyper- 
bolic beams, whether they are evenly distributed all 
round, or in groups only. 7. Whether the dark intervals 
between such radiating beams are constant or fluctuating. 
8. Whether it is concentric with the moon. 9. Whether 
it is equally intense all round the moon. 10. Whether 
the outer border exhibits any coruscations, or whether its 
definition is permanent and equally pronounced all round. 
11. Whether the light of the Corona is more intense or 
less so in the immediate neighbourhood of the promi- 
nences. 12. How much darker the moon’s disc is than 
the sky. 

! 
| 

ENERGY, AND PROF, BAIN’S LOGIC 
[EXTRACT FROM PROF. TAIT’S OPENING ADDRESS TO 
THE UNIVERSITY OF EDINBURGH, Nov. 1870] 
2; 
HE so-called Laws of Motion first explicitly stated, as 
we now employ them, by Newton in the Principia, are 
partly due to Galileo, partly to his immediate successors. 
Like all great physical discoveries, they were more or less 
clearly seen by many philosophers about the time in 
which Newton threw them into the simple, and yet 
comprehensive, form in which we now use them, As 
ordinarily understood, they embrace the results of ob- 
servation and experiment as to the action of force on 
matter. The first tells us how matter behaves when 
not acted on by force, and therefore shows us how 
to defect the action of a force. The second tells us how 
to measure the force by its effects, and how to calculate 
the action of a force or forces acting on a mere farticle of 
matter. The third, as directly interpreted, shows how to 
apply the other two to the motion of masses or of groups 
of particles. With these alone we have the foundation of 
an enormous portion of the science of Dynamics, and we 
require merely a sufficiently powerful mathematical pro- 
cess to enable us to develop to their utmost the calcula- 
tions necessary for the determination of equilibrium or 
motion of any set of masses whatever, so long as the 
motion is visible, or capable of being rendered visible by 
a microscope. 
But we require something more before we can extend 
mathematical calculations—which, be it ever remembered, 
are necessary in physics solely on account of the imper- 
fections of our intellect ; merely saving us an intolerable 
amount of thought which would otherwise be wasted on 
petty details—something more, I say, is required before we 
can apply our mathematics to Heat, Electricity, Chemical 
Action, &c., &c. 
Curiously enough, that something was foreseen and pro- 
vided for by the keen intellect of Newton. He gave it in 
the form of a second mode of interpreting his third law, 
quite distinct from the ordinary one, which is the well- 
known assertion that “Action and Reaction are equal 
and opposite.” Instead of using the terms Action and 
Reaction in the sense of mere pressures or tensions, he 
shows that the law will equally hold if they stand for 
what are now called rates of spending or of receiving 
energy ; or, in more familiar language, rates of doing work. 
So that whenever there is transference of energy from one 
body to another, the one gains exactly as much as the 
otherloses. This is at present the grandest physical law 
known. That we may understand it better, let us take first 
a simple physical fact, but one of a somewhat analogous 
nature. It is a comparatively recent discovery that master 
7s indestructible, yet so important that without it we may 
be certain that chemistry could never have become a 
science. Ifa chemist were not assured by experiment 
that no quantity of matter, however small, is ever put out 
of existence, submit it to what ordeals he may, what con- 
fidence could he have in the results of an analysis? Or 
again, where would his science be if new matter could 
suddenly make its appearance? The balance is his most 
important instrument, but without the confidence (derived 
from experiment) that matter cannot change in quantity, 
its indications would be of no va!ue to him. 
So it is, but in a more extended sphere, with the 
| Natural Philosopher, and it is a source of legitimate 
pride to us, that as Newton first hinted at this grand 
modern generalisation, and first gave the mathematical 
method naturally fitted for its development, so it is to 
this country again, and mainly to Dr. Joule of Man- 
chester, that we owe the proof (which must, of course, 
be experimental to be valid) that energy is, like matter, 
indestructible. It is, therefore, in the usual sense of 
the word, as REAL as matter. In fact, the physical 
phenomena of the Universe (excluding in the meantime, 
on account of our utter ignorance, some of those con- 
nected with hfe) depend upon matter and energy alone. 
Different combinations of matter constitute the subject 
of our chemistry ; different groupings of molecules as 
well-as of masses, and different distribution of Energy, 
| form the rest of our Natural Philosophy. Hence the 
overwhelming importance of this real something, Energy, 
in the whole of Physical Science. 
I shall devote the rest of my time this morning to very 
elementary notions connected with energy and this grand 
law of Nature. But before I do so I have a few words to 
say about another work in which the principles of Natural 
Philosophy are discussed ; a book infinitely more likely than 
that of Hegel (whose absurdities I have already pointed 
out to you) to fall into your hands. It is now not a dreamy 
and dogmatic German, evolving everything from himself, 
and railing at physical facts as well as at exquisite methods 
in mathematics, with whom we have to do—it is on the 
contrary, a hard-headed Scotsman, and a Professor in one 
of our Universities. We have here no evolution from 
consciousness to laugh at, no sneering at experimental 
science ; we have to guard against dangerous misconcep- 
tions of the truths discovered by physicists ; mistakes all 
the more dangerous that they are honestly held, and that 
they have been assigned a prominent place in a text- 
book which many of you may have at some time to read ; 
and especially because, as students, you are peculiarly 
liable to be led away by ex cathedrd statements. For 
obvious reasons I cannot take many examples now; in 
the more abstruse, the statement itself, and the exposition 
of its error, would be alike unintelligible to you; in the 
simpler ones you may be trusted to see the error for your- 
selves. 
The first I quote is from what is called the Logic of 
Physics, and is, toa certain extent, personal. “ Volume 
and wzass rightly precede denszty in order of definition. 
Messrs. Thomson and Tait make density precede mass.” 
And we do so, we think, very logically, because density is a 
specific property of matter, unalterable in general, except 
to avery small extent, by physical processes, while volume 
and mass are absolutely indefinite, depending as they do 
upon the quantity of matter spoken of. 
Again, “ In the transfer of force, xothing is fost. The 
mechanical momentum transmuted into heat is fully 
accounted for in the heat produced : by proper arrange- 
ments it could all be gained back.” The last nine words, 
however they may be interpreted, are essentially false : in 
fact they contain an explicit denial of the second law of 
thermodynamics upon which Sir W. Thomson based his 
| grand law of Dissipation of Energy, one of the most 1m- 

