This is what Popper has to say about Hegel (note 1: everything below this paragraph came from Popper’s book; note 2: I formatted the paragraph for clarity.):
“In order to discourage the reader beforehand from taking Hegel’s bombastic and mystifying cant too seriously, I shall quote some of the amazing details which he discovered about sound, and especially about the relations between sound and heat. I have tried hard to translate this gibberish from Hegel’s Philosophy of Nature as faithfully as possible; he writes:
‘§302. Sound is the change in the specific condition of segregation of the material parts, and in the negation of this condition;—merely an abstract or an ideal ideality, as it were, of that specification. But this change, accordingly, is itself immediately the negation of the material specific subsistence; which is, therefore, real ideality of specific gravity and cohesion, i.e.—heat. The heating up of sounding bodies, just as of beaten or rubbed ones, is the appearance of heat, originating conceptually together with sound.’
There are some who still believe in Hegel’s sincerity, or who still doubt whether his secret might not be profundity, fullness of thought, rather than emptiness. I should like them to read carefully the last sentence (which is the only intelligible one) of this quotation, because in this sentence Hegel gives himself away. For clearly, it means nothing but: ‘The heating up of sounding bodies . . is heat . . together with sound.’
The question arises whether Hegel deceived himself, hypnotized by his own inspiring jargon, or whether he boldly set out to deceive and bewitch others. I am satisfied that the latter was the case, especially in view of what Hegel wrote in one of his letters. In this letter, dated two years before the publication of his Philosophy of Nature, Hegel referred to another Philosophy of Nature, written by his good friend Schelling:
‘I have had too much to do . . with mathematics . . differential calculus, chemistry’,
Hegel boasts in this letter (but this is just bluff), ‘to let myself be taken in by the humbug of the Philosophy of Nature, by this philosophizing without knowledge of fact . . and by the treatment’ of mere fancies, even imbecile fancies, as ideas.’ This is a very fair characterization of Schelline’s method, that is to say, of that impudent and audacious way of bluffing which Hegel himself copied, or rather exploited and aggravated, as soon as he realized that if it reached its proper audience it meant success.”
The Open Society and Its Enemies Volume 2: Hegel and Marx by Karl Raimund Popper (Originally published 1945) (Edition extracts taken from version published by Routledge and Kegan Paul, 5th Edition, 1973 reprint, ISBN 0 7100 4626 X) (Page 28)