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Home > Dictionary of Science Quotations > Scientist Names Index M > James Clerk Maxwell Quotes > Energy

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James Clerk Maxwell
(13 Jun 1831 - 5 Nov 1879)

Scottish mathematician and physicist whose researches united electricity and magnetism into the concept of the electro-magnetic field.


James Clerk Maxwell Quotes on Energy (7 quotes)

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Any opinion as to the form in which the energy of gravitation exists in space is of great importance, and whoever can make his opinion probable will have, made an enormous stride in physical speculation. The apparent universality of gravitation, and the equality of its effects on matter of all kinds are most remarkable facts, hitherto without exception; but they are purely experimental facts, liable to be corrected by a single observed exception. We cannot conceive of matter with negative inertia or mass; but we see no way of accounting for the proportionality of gravitation to mass by any legitimate method of demonstration. If we can see the tails of comets fly off in the direction opposed to the sun with an accelerated velocity, and if we believe these tails to be matter and not optical illusions or mere tracks of vibrating disturbance, then we must admit a force in that direction, and we may establish that it is caused by the sun if it always depends upon his position and distance.
— James Clerk Maxwell
Letter to William Huggins (13 Oct 1868). In P. M. Hannan (ed.), The Scientific Letters and Papers of James Clerk Maxwell (1995), Vol. 2, 1862-1873, 451-2.
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Available energy is energy which we can direct into any desired channel. Dissipated energy is energy which we cannot lay hold of and direct at pleasure, such as the energy of the confused agitation of molecules which we call heat. Now, confusion, like the correlative term order, is not a property of material things in themselves, but only in relation to the mind which perceives them. A memorandum-book does not, provided it is neatly written, appear confused to an illiterate person, or to the owner who understands it thoroughly, but to any other person able to read it appears to be inextricably confused. Similarly the notion of dissipated energy could not occur to a being who could not turn any of the energies of nature to his own account, or to one who could trace the motion of every molecule and seize it at the right moment. It is only to a being in the intermediate stage, who can lay hold of some forms of energy while others elude his grasp, that energy appears to be passing inevitably from the available to the dissipated state.
— James Clerk Maxwell
'Diffusion', Encyclopaedia Britannica (1878). In W. D. Niven (ed.), The Scientific Papers of James Clerk Maxwell (1890), Vol. 2, 646.
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Force, then, is Force, but mark you! Not a thing,
Only a Vector;
Thy barbθd arrows now have lost their sting,
Impotent spectre!
Thy reign, O force! is over. Now no more
Heed we thine action;
Repulsion leaves us where we were before,
So does attraction.
Both Action and Reaction now are gone.
Just ere they vanished,
Stress joined their hands in peace, and made them one;
Then they were banished....
— James Clerk Maxwell
Reproduced in Bruce Clarke, Energy Forms: Allegory and Science in the Era of Classical Thermodynamics (2001), 20-21. In his parody of Shelley's Prometheus Unbound, Maxwell presents Newton's laws of motion updated into axioms of energy.
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In fact, whenever energy is transmitted from one body to another in time, there must be a medium or substance in which the energy exists after it leaves one body and before it reaches the other ... and if we admit this medium as an hypothesis, I think it ought to occupy a prominent place in our investigations, and that we ought to endeavour to construct a mental representation of all the details of its action, and this has been my constant aim in this treatise.
— James Clerk Maxwell
A Treatise on Electricity and Magnetism (1873), Vol. 2, 438.
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That small word “Force,” they make a barber's block,
Ready to put on
Meanings most strange and various, fit to shock
Pupils of Newton....
The phrases of last century in this
Linger to play tricks—
Vis viva and Vis Mortua and Vis Acceleratrix:
Those long-nebbed words that to our text books still
Cling by their titles,
And from them creep, as entozoa will,
Into our vitals.
But see! Tait writes in lucid symbols clear
One small equation;
And Force becomes of Energy a mere
Space-variation.
— James Clerk Maxwell
'Report on Tait's Lecture on Force:— B.A., 1876', reproduced in Bruce Clarke, Energy Forms: Allegory and Science in the Era of Classical Thermodynamics (2001), 19. Maxwell's verse was inspired by a paper delivered at the British Association (B.A.. He was satirizing a “considerable cofusion of nomenclature” at the time, and supported his friend Tait's desire to establish a redefinition of energy on a thermnodynamic basis.
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To pick a hole–say in the 2nd law of Ωcs, that if two things are in contact the hotter cannot take heat from the colder without external agency.
Now let A & B be two vessels divided by a diaphragm and let them contain elastic molecules in a state of agitation which strike each other and the sides. Let the number of particles be equal in A & B but let those in A have equal velocities, if oblique collisions occur between them their velocities will become unequal & I have shown that there will be velocities of all magnitudes in A and the same in B only the sum of the squares of the velocities is greater in A than in B.
When a molecule is reflected from the fixed diaphragm CD no work is lost or gained.
If the molecule instead of being reflected were allowed to go through a hole in CD no work would be lost or gained, only its energy would be transferred from the one vessel to the other.
Now conceive a finite being who knows the paths and velocities of all the molecules by simple inspection but who can do no work, except to open and close a hole in the diaphragm, by means of a slide without mass.
Let him first observe the molecules in A and when lie sees one coming the square of whose velocity is less than the mean sq. vel. of the molecules in B let him open a hole & let it go into B. Next let him watch for a molecule in B the square of whose velocity is greater than the mean sq. vel. in A and when it comes to the hole let him draw and slide & let it go into A, keeping the slide shut for all other molecules.
Then the number of molecules in A & B are the same as at first but the energy in A is increased and that in B diminished that is the hot system has got hotter and the cold colder & yet no work has been done, only the intelligence of a very observant and neat fingered being has been employed. Or in short if heat is the motion of finite portions of matter and if we can apply tools to such portions of matter so as to deal with them separately then we can take advantage of the different motion of different portions to restore a uniformly hot system to unequal temperatures or to motions of large masses. Only we can't, not being clever enough.
— James Clerk Maxwell
Letter to Peter Guthrie Tait (11 Dec 1867). In P. M. Harman (ed.), The Scientific Letters and Papers of James Clerk Maxwell (1995), Vol. 2, 331-2.
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[Helmholtz] is not a philosopher in the exclusive sense, as Kant, Hegel, Mansel are philosophers, but one who prosecutes physics and physiology, and acquires therein not only skill in developing any desideratum, but wisdom to know what are the desiderata, e.g., he was one of the first, and is one of the most active, preachers of the doctrine that since all kinds of energy are convertible, the first aim of science at this time. should be to ascertain in what way particular forms of energy can be converted into each other, and what are the equivalent quantities of the two forms of energy.
— James Clerk Maxwell
Letter to Lewis Campbell (21 Apr 1862). In P.M. Harman (ed.), The Scientific Letters and Papers of James Clerk Maxwell (1990), Vol. 1, 711.
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Carl Sagan Thumbnail In science it often happens that scientists say, 'You know that's a really good argument; my position is mistaken,' and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time something like that happened in politics or religion. (1987) -- Carl Sagan
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