Letters of Euler on Different Subjects in Natural Philosophy: Addressed to a German Princess, Volumen1

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J. & J. Harper, 1833 - 819 páginas
 

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Página 142 - ... the angle of reflection is always equal to the angle of incidence, the image for any point can be seen only in the reflected ray prolonged.
Página 233 - we are reduced to explain what is to be understood by the term matter, without which extension cannot be body. Now, the signification of these two terms is so much the same, that all body is matter, and all matter is body ; so that even now we have made no great progress. We easily discover, however, a general character, inseparable from all matter, and consequently pertaining to all bodies ; it is impenetrability, the impossibility of being penetrated by other bodies, or the impossibility that...
Página 112 - And rays which make such a number of vibrations in a second may, with equal propriety, be denominated red rays ; and finally, when the optic nerve is affected by these same rays, and receives from them a number of impulsions, sensibly equal, in a second, we receive the sensation of the red colour. Here every thing is clear ; and I see no necessity for introducing dark and mysterious phrases, which really mean nothing.
Página 298 - ... was disposed in perfect harmony with all these circumstances. When, therefore, a man addresses to God a prayer worthy of being heard, it must not be imagined that such a prayer came not to the knowledge of God till the moment it was formed.
Página 112 - When 1 produced the phenomenon of a musical chord, which may be excited into vibration by the resonance only of certain sounds, you will please to recollect, that the one which gives the unison of the chord in question is the most proper to shake it, and that other sounds affect it only in proportion as they are in consonance with it. It is exactly the same as to light and colours ; for the different colours correspond to the different musical sounds.
Página 229 - Every one readily admits, that all these would fall downwards, unless they were supported. Now, the question turns on the real cause of this fall. Some say that it is the earth which attracts these bodies, by an inherent power natural to it ; others, that it is the ether, or some other subtile or invisible matter, which impels the body downwards : so that the effect is, nevertheless, the same in both cases. This last opinion is most satisfactory to those who are fond of clear principles in philosophy,...
Página 37 - But with regard to our ear, there are certain limits beyond which sound is no longer perceptible. It would appear that we are incapable of determining either the sound of a string which makes less than 30 vibrations in a second, because it is too low ; or that of a string which would make more than 7552 in a second, because such a note would be too high.* 26th April, 1760.
Página 297 - God a prayer worthy of being heard it must not be imagined that such a prayer came not to the knowledge of God till the moment it was formed. That prayer was already heard from all eternity; and if the Father of Mercies deemed it worthy of being answered, he arranged the world expressly in favor of that prayer, so that the accomplishment should be a consequence of the natural course of events.
Página 19 - Reichenbach ; and he was soon after presented to the queen-mother, a princess who took great pleasure in the conversation of illustrious men. She treated Euler with the utmost familiarity ; but never being able to draw him into any conversation but that of monosyllables, she one day asked him why he did not wish to speak to her 1 " Madam," replied Euler, " it is because I have just come from a country where every person who speaks is hanged.
Página 214 - ... however, not precisely six hours, but about eleven minutes more; so that the time of high water does not always happen at the same hour, but is about three quarters of an hour later every day, for thirty days, when it again recurs as before. For example, if it be high water...

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