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History of Vegetarianism - Europe: The Middle Ages to the 18th Century
Sir Isaac Newton (1642-1727)

English mathematician, physicist, astrononer, and philosopher, noted particularly for his law of gravitation, his three laws of motion, his theory that light is composed of corpuscles, and his development of calculus independently of Leibntz. His works include Principia Mathematica (1687) and Optiks (1704)

The following was contributed by Cooke Kelsey, from Florida:

There has long been a rumor that Newton was vegetarian, although none of his biographies mention anything on the subject, so I wrote to his biographers to see if there was anything in the primary sources. I received this reply from Dr. Patricia Fara, a Newton scholar at Cambridge University: "I have heard the rumour, but the evidence suggests that he did eat meat except for the last five years of his life, when he was quite frail and followed a light diet which might perhaps have been vegetarian."

I have received the following note from the American Newton scholar Gale Christianson: "Newton did tend to eat vegetables and broth when he was an old man, but there is nothing to indicate that he was a conscious vegetarian...during the early and middle years."

Finally, James Gleick, the famous writer of 'Chaos' recently wrote a book about Newton. I asked him if he knew of the long-held rumor that he was vegetarian. He replied, "The 'rumor' started with his niece, who said he was reluctant to eat meat in later life. It's just one data point. Hardly anything is known about what he ate except that he didn't care much about meals."

About Isaac Newton
 [info from Nuno Metello, Portugal]

Voltaire, a contemporary, wrote about Newton’s compassion for animals:

There is in man a disposition to compassion as generally diffused as his other instincts. Newton had cultivated this sentiment of humanity, and he extended it to lower animals. With Locke he was strongly convinced that God has given to them a proportion of ideas, and the same feelings which he has to us. He could not believe that God, who has made nothing in vain, would have given to them organs of feeling in order that they might have no feeling.

He thought it a very frightful inconsistency to believe that animals feel and at the same time to cause them to suffer. On this point his morality was in accord with is philosophy. He yielded but only with repugnance to the barbarous custom of supporting ourselves upon the blood and flesh of beings like ourselves, whom we caress, and he never permitted in his own house the putting them to death by slow and exquisite modes of killing for the sake of making the food more delicious. This compassion, which he felt for no other animals, culminated in true charity for men. In truth, without humanity, a virtue which comprehends all virtues, the name of philosopher would be little deserved. (Voltaire, Elements de la Philosophie de Newton, 1741, V., quoted in Howard Williams, The Ethics of Diet, University of Illinois Press, 2003, p. 145).

In his book Vegetable Diet: As Sanctioned by Medical Men and by Experience in All Ages (1869), Dr. William A. Alcott writtes the following about Newton:

This distinguished philosopher and mathematician is said to have abstained rigorously, at times, from all but purely vegetable food, and from all drinks but water; and it is also stated that some of his important labors were performed at these seasons of strict temperance. While writing his treatise on Optics, it is said he confined himself entirely to bread, with a little sack and water; and I have no doubt that his remarkable equanimity of temper, and that government of his animal appetites, throught, for which he was so distinguished to the last hour of his life, were owing, in no small degree, to his habits of rigid temperance (p. 191).

In a footnote to The Ethics of Diet, 1883, p.145 of the first edition, Howard Williams notes:

Haller [Albrecht von Haller M.D. 1708-1777], the founder of modern physiology, assures us that "Newton, while he was engaged upon his Optics, lived almost entirely on bread, and wine, and water" (Newtonus, dum Optica scribebat, solo pœmé et aqua vixit). - Elements of Physiology, vi., 198