I give the memorable account, as Boyle has delivered it, of the circumstances which led Harvey to the discovery of the circulation of the blood.
“I remember that when I asked our famous Harvey, in the only discourse I had with him, which was but a little while before he died, what were the things which induced him to think of a circulation of the blood, he answered me, that when he took notice that the valves in the veins of so many parts of the body were so placed that they gave free passage to the blood towards the heart, but opposed the passage of the venal blood the contrary way, he was invited to think that so provident a cause as nature had not placed so many valves without design; and no design seemed more probable than that, since the blood could not well, because of the interposing valves, be sent by the veins to the limbs, it should be sent through the arteries and return through the veins, whose valves did not oppose its course that way.”
The reason here ascribed to Harvey seems now so very natural and obvious, that some have been disposed to question his claim to the high rank commonly assigned to him among the improvers of science! Dr. William Hunter has said that after the discovery of the valves in the veins, which Harvey learned while in Italy from his master, Fabricius ab Aquapendente, the remaining step might easily have been made by any person of common abilities. “This discovery,” he observes, “set Harvey to work upon the use of the heart and vascular system in animals; and in the course of some years, he was so happy as to discover, and to prove beyond all possibility of doubt, the circulation of the blood.” He afterwards expresses his astonishment that this discovery should have been left for Harvey, though he acknowledges it occupied “a course of years;” adding that “Providence meant to reserve it for him, and would not let men see what was before them, nor understand what they read.” It is remarkable that when great discoveries are effected, their simplicity always seems to detract from their originality: on these occasions we are reminded of the egg of Columbus!
It is said that a recent discovery, which ascertains that the Niger empties itself into the Atlantic Ocean, was really anticipated by the geographical acumen of a student at Glasgow, who arrived at the same conclusion by a most persevering investigation of the works of travellers and geographers, ancient and modern, and by an examination of African captives; and had actually constructed, for the inspection of government, a map of Africa, on which he had traced the entire course of the Niger from the interior.
Franklin conjectured the identity of lightning and of electricity, before he had realised it by decisive experiment. The kite being raised, a considerable time elapsed before there was any appearance of its being electrified. One very promising cloud had passed over it without any effect. Just as he was beginning to despair of his contrivance, he observed some loose threads of the hempen string to stand erect, and to avoid one another, just as if they had been suspended on a common conductor. Struck with this promising appearance, he immediately presented his knuckle to the key! And let the reader judge of the exquisite pleasure he must have felt at that moment when the discovery was complete! We owe to Priestley this admirable narrative; the strong sensation of delight which Franklin experienced as his knuckle touched the key, and at the moment when he felt that a new world was opening, might have been equalled, but it was probably not surpassed, when the same hand signed the long-disputed independence of his country!
When Leibnitz was occupied in his philosophical reasonings on his Law of Continuity, his singular sagacity enabled him to predict a discovery which afterwards was realised—he imagined the necessary existence of the polypus!
It has been remarked of Newton, that several of his slight hints, some in the modest form of queries, have been ascertained to be predictions, and among others that of the inflammability of the diamond; and many have been eagerly seized upon as indisputable axioms. A hint at the close of his Optics, that “If natural philosophy should be continued to be improved in its various branches, the bounds of moral philosophy would be enlarged also,” is perhaps among the most important of human discoveries—it gave rise to Hartley’s Physiological Theory of the Mind. The queries, the hints, the conjectures of Newton, display the most creative sagacity; and demonstrate in what manner the discoveries of retired men, while they bequeath their legacies to the world, afford to themselves a frequent source of secret and silent triumphs.
[263] The remarkable clue to the reading of the hieroglyphic language of ancient Egypt perfected in our own times is a striking instance of this; as well as the investigations now proceeding in Babylonian inscriptions, which promise to enable us to comprehend a language that was once considered as hopelessly lost.
[264] The curious reader may view the marks, and the manner in which the Greek characters were made out, in the preface to Hearne’s “Curious Discourses.” The amethyst proved more difficult than the frieze, from the circumstance, that in engraving on the stone the letters must be reversed.