The total quantity of all the forces capable of work in the whole universe remains eternal and unchanged throughout all their changes. All change in nature amounts to this, that force can change its form and locality, without its quantity being changed. The universe possesses, once for all, a store of force which is not altered by any change of phenomena, can neither be increased nor diminished, and which maintains any change which takes place on it.
Interpretation
The universe's total energy remains constant, despite changes in its form or location.
This quote emphasizes the conservation of energy principle, asserting that while energy can transform from one form to another, the total amount remains unchanged. Hermann Von Helmholtz highlights that the forces at play in the universe are eternal and invariant, underlying all changes and phenomena, suggesting a fundamental law of nature which assures that the sum of energy is preserved regardless of its manifestations.
In practice
In a lecture about physics, you could quote this to explain the conservation of energy.
Isolated facts and experiments have in themselves no value, however great their number may be. They only become valuable in a theoretical or practical point of view when they make us acquainted with the law of a series of uniformly recurring phenomena, or, it may be, only give a negative result showing an incompleteness in our knowledge of such a law, till then held to be perfect.
Black is real sensation, even if it is produced by entire absence of light. The sensation of black is distinctly different from the lack of all sensations.
Whoever, in the pursuit of science, seeks after immediate practical utility, may generally rest assured that he will seek in vain.
Burning carbon-based substances like oil, gas, and especially coal, produces billions of tons of extra carbon dioxide each year. Methane gas from cows and pigs and other animals on our large farms ends up in the atmosphere as well, trapping more of the sun's energy as heat.
Throughout history, people have studied pure science from a desire to understand the universe rather than practical applications for commercial gain. But their discoveries later turned out to have great practical benefits.
Medicine is a science which hath been (as we have said) more professed than laboured, and yet more laboured than advanced: the labour having been, in my judgment, rather in circle than in progression. For I find much iteration, but small addition. It considereth causes of diseases, with the occasions or impulsions; the diseases themselves, with the accidents; and the cures, with the preservation.
Since, then, there is no objection to the mobility of the Earth, I think it must now be considered whether several motions are appropriate for it, so that it can be regarded as one of the wandering stars. For the fact that it is not the centre of all revolutions is made clear by the apparent irregular motion of the wandering stars, and their variable distances from the Earth, which cannot be understood in a circle having the same centre as the Earth.
Our science fails to recognize those special properties of life that make it fundamental to material reality. This view of the world - biocentrism - revolves around the way a subjective experience, which we call consciousness, relates to a physical process. It is a vast mystery and one that I have pursued my entire life.
It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.
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