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26 [42] HEROPHILUS ERASISTRATUS [43] Aristarchus had no instruments capable of measuring angles accurately and his estimates of what those angles must be were rather off. He concluded that the sun was about twenty times as far as the moon, whereas in fact it is about four hundred times as far. Aristarchus then worked out the actual size of the moon by noting the size of the shadow thrown by the earth during an eclipse of the moon. By a correct line of argument, again marred by the inac curacy of his measurements, he con cluded that the moon had a diameter one-third that of the earth. This is only a slight overestimate. If the sun were twenty times as distant as the moon, and yet the same size in appearance, it must be twenty times the diameter of the moon or about seven times the diameter of the earth. Actually we now know the sun is over a hundred times the diameter of the earth, but even Aristarchus’ too-small value was enough to make it seem illogi cal, to him, that the sun revolved about the earth. It seemed to him that the smaller object should revolve about the larger.
Unfortunately this logic, which seemed so solid to him (and which seems so solid to us), did not impress his contem poraries. [42] HEROPHILUS (hee-rof ih-lus) Greek anatomist Born: Chalcedon (the modern Kadikoy, a suburb of Istanbul, Turkey), about 320 b . c .
The biological sciences as well as the physical ones reached new heights in Alexandria’s early days. Working there, Herophilus, who may have studied under Praxagoras [36], established himself as the first careful anatomist and the first to perform dissections in public, perhaps as many as six hundred altogether. He la bored hard to compare the human mech anism with that of animals. There was no serious objection among the Greeks to anatomical dissections in those pre Christian days and indeed the Platonic view was that the body of man meant very little in comparison with his soul. The dead body was then a mere lump of flesh that could be cut with impunity. To the Egyptian natives, however, human dissection was a serious impiety. (Some centuries later the early Christian Fa thers held it as an example of pagan cru elty that vivisections—the dissections of living bodies—were performed. This was taken from statements by Celsus [57] and was probably exaggeration. It seems quite certain that deliberate vivisection was not practiced. Even ordinary dissec tion of dead bodies was all too limited, or the ancients wouldn’t have made some of their anatomical errors.) Herophilus was particularly interested in describing the brain. He divided nerves into sensory (those which re ceived sense impressions) and motor (those which stimulated motion). He also described the liver and spleen. He described and named the retina of the eye and he named the first section of the small intestine, the duodenum. His inves tigation of the genital system led to a de scription of the ovaries and of the tubes leading to the ovaries from the uterus. He also observed and named the prostate gland.
He noted that arteries, unlike veins, pulsate and timed the pulsations with a water clock, but he failed to see the con nection between this arterial pulse and the heartbeat. He held that the arteries carried blood and he also felt that blood letting had therapeutic value. This em phasis on bleeding was to have a dele terious effect on medicine for two thou sand years. His work was worthily car ried on by his successor Erasistratus [43], but thereafter the Alexandrian school of anatomy declined. [43] ERASISTRATUS (er-uh-sis'tra-tus) Greek physician
gean island), about 304 B.c. Died: Mycale, ab o u t 250 b
c . Erasistratus, according to tradition, was trained in Athens, then traveled to Asia where he served as court physician 27 [43] ERASISTRATUS PHILON [45] for Seleucus I, who controlled the major portion of what had once been the Per sian Empire. Erasistratus then moved west, where he continued the work of Herophilus [42] at Alexandria. In later life, Erasis tratus devoted himself to research and, according to tradition, committed suicide when afflicted with an incurable ulcer in the foot. He, too, paid particular attention to the brain, which he described as being divided into a larger (cerebrum) and smaller (cerebellum) part. He compared the convolutions in the brain of man with those of animals and decided (cor rectly) that the complexity of the con volutions was related to intelligence. He noticed the association of nerves with arteries and veins and imagined that each organ of the body was fed by all three, each of them, nerve, artery, and vein, bringing its own fluid to the organ. The nerve, which he and others of the time believed to be hollow, carried “ner vous spirit,” according to this view; the artery, “animal spirit”; and the vein, blood. He took a step backward from Herophilus’ views by denying that the arteries carried blood. On the other hand, he believed that air was carried from the lungs to the heart and changed into the “animal spirit” that was carried in the arteries. If we remember that it is oxygen that is carried by the blood and relate oxygenated hemoglobin with “ani mal spirit” and ordinary hemoglobin with blood, his views are not so wrong. The difference is mainly one of seman tics. In fact, Erasistratus came near to grasping the notion of the circulation of the blood, but not quite. That concept had to wait two millennia for Harvey [174]. He also refused to accept the er roneous humor theory of disease which had been made popular by Hippocrates [22]. Unfortunately, Galen [65] returned to it and that proved decisive for the next fifteen centuries. Tradition makes Erasistratus a grand son of Aristotle [29] and a pupil of Theophrastus [31]. If so, he broke with his grandfather’s views and accepted the atomism of Democritus. Indeed, Erasis- tratus believed that all body functions were mechanical in nature. Digestion, for instance, he thought to result from the grinding of food by the stomach. Two thousand years later Borelli [191] was to revive this notion. Egyptian objections to human dissec tion prevailed, however, and after the promising start made by Herophilus and Erasistratus, the study of anatomy de clined, not to be revived until the time of Mondino de’ Luzzi [110], fifteen cen turies later. [44] CONON (koh'non) Greek mathematician
b . c .
Conon was a pupil of Euclid [40], ac cording to tradition, and a teacher of Archimedes [47], It is possible that the mathematical curve usually ascribed to Archimedes and called, therefore, the “spiral of Archimedes” was actually first studied by Conon. Conon is best known for a piece of conscienceless flattery. It seems that about 245 b .
., Ptolemy III, king of Egypt, was off to the wars and Berenice, his queen, dedicated her hair at the tem ple of Aphrodite in order to persuade that goddess to bring him home safe and victorious. The hair disappeared, undoubtedly sto len by souvenir hunters, but Conon smoothly assured the sorrowing queen that Aphrodite had snatched the hair up to heaven where it now hung as a brand- new constellation. He pointed out a group of dim stars not previously hon ored by the attention of astronomers and that group is known as Coma Berenices (“Berenice’s Hair”) to this day. [45] PHILON (figh'lon) Greek engineer
b . c .
Like Hero [60], Philon experimented with air in a decidedly modem fashion and came to conclusions that were re
[46] CTEsmrus ARCHIMEDES [47] markable but were ignored by the philos ophers of the time. He found that air expanded with heat, and he may even have groped toward the beginnings of an air thermometer as Galileo [166] was to do thirteen cen turies later. He also found that some air in a closed vessel was consumed by a burning torch, an observation from which Lavoisier [334] was to draw revo lutionary conclusions fifteen centuries later. He studied catapults carefully and since these were war weapons, those re searches were given more notice. He also wrote on the art of besieging a city and of defending it against siege. A book he wrote on secret messages and cryp tography is lost. [46] CTESIBIUS (teh-sib'ee-us) Greek inventor Born: about 300 b . c .
Ctesibius founded the engineering tra dition at Alexandria, a tradition which was to reach its peak with Hero [60] one century later. In the intellectually arro gant Greek world, Ctesibius came by his practical interests legitimately, for he was the son of a barber and his first in vention was for his father’s benefit. He supplied the barber’s mirror with a lump of lead as a counterweight so that it could more easily be raised and lowered. The lead counterweight was concealed in a pipe, and when it moved rapidly through the pipe a squeaking noise was made. It occurred to Ctesibius that a musical instrument could be built on this basis. He therefore constructed a water organ in which air was forced through different organ pipes not by a falling lead weight, but by the weight of water. He made use of weights of water and of compressed air in other ways as well, to construct an air-powered catapult, for in stance. He undoubtedly had the “feel” of a mechanical age, but he lacked the proper inanimate power to work with. Hero was to discover steam power but by then the moment had passed, not to return until the time of Newcomen [243] and Watt [316] some seventeen centuries later. The most famous invention of Ctesib ius, however, was his improvement of the ancient Egyptian clepsydra, or water clock. In this, water dripping into a con tainer at a steady rate raised a float which held a pointer that marked a posi tion on a drum. From that position the hour could be read. The drum was in geniously adjusted so that it could be used at various times of the year. (The day and night were each divided into twelve equal hours at all times, which meant that in summer the hours of day were long and those of night were short, while in winter it was the other way around.) The water clock was the best of the ancient timepieces. The mechanical clocks of the Middle Ages, run by falling weights, were more convenient, but no more accurate. It was not until the pen dulum clock of Huygens [215], eighteen centuries after the time of Ctesibius, that the clepsydra was finally outclassed. None of Ctesibius’ writings have sur vived and we know of him only through references in Vitruvius [55] and Hero. [47] ARCHIMEDES (ahr-kih-mee'deez) Greek mathematician and engi neer
B.C.
Died: Syracuse, ab o ut
212 b . c . Archimedes, the son of an astronomer, was the greatest scientist and mathe matician of ancient times, and his equal did not arise until Newton [231] two thousand years later. Archimedes studied in Alexandria, where his teacher Conon [44] had, in his own time, been a pupil of Euclid [40]. In an unusual move for those days, Archimedes chose not to remain there but to return to his native town. This may have been the result of his relationship with the Syracusan king, Hieron II. Archimedes was an aristocrat and a man of independent means and did not require the support of the Egyp tian royal house for his work. No scientist of ancient times, not even 29 [47] ARCHIMEDES ARCHIMEDES [47] Thales [3], had so many stories told about him; and all the stories are so good that it seems cruel to question then- authenticity. As a small example, tales of his absent-mindedness were lovingly re tailed and it was said that in concen trating on his thoughts, he could not remember whether he had eaten or not. (Similar stories are told of more recent mathematicians, such as Newton and Wiener [1175]). To pass on to something of impor tance, however, Hieron was supposed to have asked his bright relative to deter mine whether a crown just received from the goldsmith was really all gold, as it was supposed to be, or whether it con tained a grafting admixture of silver. Archimedes was strictly warned to make the determination without damaging the crown.
Archimedes was at a loss as to how to proceed until one day, stepping into his full bath, he noted that the water overflowed. In a flash it occurred to him that the amount of water that overflowed was equal in volume to that portion of his body which was inserted into the bath. Well, then, if he dipped the crown into water, he could tell by the rise in water level the volume of the crown. He could compare that with the volume of an equal weight of gold. If the volumes were equal, the crown was pure gold. If the crown had an admixture of silver (which is bulkier than gold), it would have a greater volume. Excited beyond measure by the discov ery of this “principle of buoyancy,” Ar chimedes dashed out of the bath and, completely naked, ran through the streets of Syracuse to the palace, shout ing, “I’ve got it! I’ve got it!” (In connec tion with this story, it is important to remember that the ancient Greeks were not as disturbed by nakedness as we are.) Since Archimedes shouted in Greek, what he said was “Eureka! Eu reka!” and that has been used ever since as the appropriate remark with which to announce a discovery. (The conclusion of the story is that the crown turned out to be partly silver and that the goldsmith was executed.) Archimedes also worked out the prin ciple of the lever. Strato [38] had made use of the principle, but it was Archi medes who worked it out in full mathe matical detail. He showed that a small weight at a distance from a fulcrum would balance a large weight near the fulcrum and that the weights and dis tances were in inverse proportion. (Thus, he founded the science of “statics” and developed the notion of a center of gravity. In thus applying the notion of quantitative measurement of weights and distances to scientific obser vations, he was two thousand years ahead of his time. In fact, it was the translation of his works into Latin in 1544 that helped inspire renewed efforts in that direction by men such as Stevinus [158] and Galileo [166].) The principle of the lever explained why a larger boulder could be pried up by a crowbar. The force at the end of the long portion of the crowbar (which is just a form of lever) balanced the force of the large weight at the end of the short portion. Archimedes made an other famous remark in this connection by saying: “Give me a place to stand on and I can move the world.” (Provided, of course, he also had a lever long enough and rigid enough.) Hieron is supposed to have questioned this remark and dared him to move something startlingly large, even if not as large as the whole world. Archimedes thereupon hooked up a system of com pound levers in pulley form, seated him self comfortably, and without undue effort (the story goes) singlehandedly pulled a fully laden ship out of the har bor and up onto the shore. Archimedes defied the tradition of art for art’s sake made popular by Plato [24] and indulged himself in intensely practi cal interests. He is supposed to have in vented a hollow, helical cylinder that, when rotated, could serve as a water pump. It is still called the “screw of Archimedes” (though, to be sure, the Egyptians are supposed to have had the device long before the time of Archi medes). Archimedes is also supposed to have designed a planetarium in which the motions of the heavenly bodies could be imitated. However, it seems that Ar
[47] ARCHIMEDES ARCHIMEDES [47] chimedes was not exactly proud of his mechanical triumphs, feeling that per haps they were not the proper work of a philosopher. He therefore published only his mathematical work. In that field, he calculated a value for pi (the ratio of the length of the circum ference of a circle to its diameter) which was better than any other obtained in the classical world. He showed that it lay be tween 22-%i and 22%o. To do this, he used a method of calculating the circum ferences and diameters of polygons de scribed inside and outside a circle. As the polygons were given more and more sides, they approached the circle in shape and area. The circumference of the inner polygon grew longer and that of the outer polygon grew shorter while the circumference of the circle was “trapped” between the two. This is very like some of the methods used in calcu lus much later, and it is often stated that Archimedes would have discovered cal culus nearly two thousand years ahead of Newton if he had only had a decent system of mathematical symbols to work with. Archimedes is also famous for a trea tise in which he calculated the number of grains of sand required to fill the en tire universe (making some guesses as to what the size of the universe was). He did this mainly to make the point that nothing real existed that was too large to be measured; or, in other words, that nothing finite was infinite. To do so, he made use of a system for expressing large numbers that is almost equivalent to our own exponential notation. Archimedes did not, however, end his days in peace. In fact, he achieved his greatest fame as a warrior. Rome had, during Archimedes’ old age, been at war with Carthage (a city of North Africa) for the second time. The Carthaginian leader was Hannibal, one of the greatest generals of history. He invaded Italy in 218
b . c . and began to enjoy remarkable success. Hieron II had a treaty of alliance with Rome and remained faithful to that treaty. He died, an extremely old man, and a grandson, Hieronymus, ruled in his place. Rome suffered a disastrous de feat at Cannae and for a time seemed about to be crushed. Hieronymus, anx ious to remain on the winning side, switched to that of Carthage. The Romans, however, were not quite through. They sent a fleet, under the general Marcellus, against Syracuse and thus began a strange three-year war of the Roman fleet against one man, Archi medes.
According to tradition the Romans would have taken the city quite quickly had it not been for the ingenious devices brought against their fleet by the great scientist. He is supposed to have con structed large lenses to set the fleet on fire, mechanical cranes to lift the ships and turn them upside down, and so on. In the end, the story goes, the Romans dared not approach the walls too closely and would flee if as much as a rope showed above it, for they were con vinced that the dreaded Archimedes was dooming them with some new and mon strous device. Much of this was undoubtedly exag gerated in the telling, for the later Greeks (such as Plutarch, from whom the story mainly stems) were only too eager to describe how Greek brains held off Roman brawn. Still, the siege was a long one and it was not until 212 b .
. that Syracuse was beaten down. (In 202 b .
. came the final victory of Rome over Carthage; the too-clever Hieronymus had guessed wrong after all.) During the sack of the city, Archi medes, with a magnificent and scholarly disregard for reality, engaged himself in a mathematical problem and was bent over the geometrical figures he had marked in the sand. A Roman soldier or dered him to come along, but Archi medes merely gestured imperiously, “Don’t disturb my circles.” The Roman soldier, apparently a prac tical man with no time for fooling, at once killed Archimedes and went on. Marcellus, who had given orders for Archimedes to be taken alive and treated with distinction (an unusual spirit of generosity for that time—or for any time, perhaps), mourned his death and directed that an honorable burial be Download 17.33 Mb. Do'stlaringiz bilan baham: 
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