82. "The nature of motion is as unknown to us as that of matter." Unlike La Mettrie, Toland holds that it is possible to know the nature of matter, and declares that motion and matter can not be defined, because their nature is self-evident. [151] Holbach, resembling La Mettrie, teaches that it is futile to seek to know the ultimate nature of matter, or the cause for its existence. "Thus if any one shall ask whence matter came, we shall say that it has always existed. If any one ask, whence came movement in matter, we shall answer that for this same reason matter must have moved from eternity, since motion is a necessary consequence of its existence, its essence, and of its primitive properties, such as extent, weight, impenetrability, shape, etc.... The existence of matter is a fact; the existence of motion is another fact." [152] 83. Huyghens (Christian) was born at The Hague, 1629, and died there in 1695. He was a Dutch physicist, mathematician, and astronomer. He is celebrated for the invention of the pendulum clock which could measure the movements of the planets, for the improvement of the telescope, and for the development of the wave-theory of light. His principal work is "Horologium Oscillatorium" (1673). [153] 84. Julien Leroy (1686-1759) was a celebrated French watchmaker. He excelled in the construction of pendulums and of large clocks. Some have attributed the construction of the first horizontal clock to him, but this is doubtful. Among many other inventions and improvements of clocks, he invented the compensating pendulum which bears his name. [154] 85. Jacques de Vaucanson (1709-1782) was a French mechanist. From his childhood he was always interested in mechanical contrivances. In 1738 he presented to the French Academy his remarkable flute player. Soon after, he made a duck which could swim, eat, and digest, and an asp which could hiss and dart on Cleopatra's breast. He later held the position of inspector of the manufacture of silk. In 1748 he was admitted to the Academy of Sciences. His machines were left to the Queen, but she gave them to the Academy, and in the disturbances which followed the pieces were scattered and lost. Vaucanson published: "Mécanisme d'un flûteur automate" (Paris, 1738). [155] 86. "[Descartes] understood animal nature; he was the first to prove completely that animals are pure machines." Contrast this with La Mettrie's former reference in "L'histoire naturelle de l'âme" to "this absurd system 'that animals are pure machines.' Such a laughable opinion," he adds, "has never gained admittance among philosophers.... Experience does not prove the faculty of feeling any less in animals than in men." [156] It is evident that La Mettrie's opposition to this 'absurd system' was based upon his insistence on the similarity of men and animals. In "L'homme machine" he argues from the same premiss, that animals are machines, that men are like animals, and that therefore men also are machines.