Eureka! Page 10

  We should not feel a childish disgust at the investigation of the meaner animals. For there is something of the marvellous in all living things.

  Aristotle had a considerable struggle to get biology accepted as a proper field of study for the scientist or philosopher. The Greeks held a strongly hierarchical conception of nature and the cosmos, such that the study of its finer parts, such as the heavens or human beings, was accepted, while the investigation of its lesser parts was seen by some to be demeaning. Aristotle’s views were very important in getting the study of animals and plants onto a serious footing. Central to this was Aristotle’s view that nature does nothing in vain, that all animals are well organised and an expression of the good.

  Embryology and Species

  Aristotle made a very detailed study of the development of animal embryos. He supported the idea of ‘epigenesis’ against those who believed in pre-formation. Epigenesis was the view that the embryo develops its different parts from an amorphous beginning, rather than having all of its parts ready formed. He argued against ‘pangenesis’, and for the fixity of species. Pangenesis was the idea that characteristics acquired during life are passed on to the offspring, e.g., if giraffes stretch their necks to feed, then baby giraffes are born with longer necks. Aristotle also argued against the ancient idea that mutilated humans produced deformed offspring. His view was that the male provides the form, the female provides the matter, and the embryo has then a potential to become an adult human, which it proceeds to actualise. Inherent in this is the idea of the fixity of species – that there is no evolution. Humans (and all other species) are what they always were (and will be), and the boundaries between species are permanent.

  Taxonomy

  A serious problem for biology in the ancient world was how to arrange species of animals into groups. Aristotle produced the first system to give a reasonable classification of animals. Rather than basing his system on organs of movement, as previous attempts had done, Aristotle used modes of reproduction. The main groups that he devised were: the viviparous, which bear live offspring; the oviparous, with perfect or imperfect eggs; and the insects, with larvae. Animals were then divided up into genus and species. The system was a hierarchy of perfection, man naturally being considered the most perfect species. The modern system of classification dates from Linnaeus in the eighteenth century.

  Theophrastus (371–286 BC) followed Aristotle as head of the Lyceum, and continued his biological work, classifying many species of plants. Many Greeks believed in the spontaneous generation of both plants and small animals (as did many people up to the eighteenth century). Theophrastus was more reserved about this, arguing that the wind carried many small seeds which could account for the generation of plants. He was also the first to make a comprehensive study and classification of rocks. Against Aristotle, he argued that there were limits to the expression of the good in nature. It seemed to him that some parts served no function (such as human male breasts), while some parts could be better arranged and some were even harmful. He did not reject teleological arguments outright by any means, but he did realise that there were limits to this sort of argument, and that many things in nature did occur by chance.

  7 Later Greek Science: After Aristotle

  … Nil posse creari

  De nilo

  (Nothing can be created out of nothing.)

  Lucretius, De Rerum Natura, book 1, l. 155

  Later Greek science and philosophy is usually taken to start with the death of Aristotle in 322 BC (and Alexander the Great in 323 BC), the beginning of the era known as the Hellenistic period. The major periods for ancient science were:

  Babylonian – 1000 BC onwards

  Pre-Socratic – 600–400 BC

  Athenian – 400–300 BC

  Hellenistic – 300 BC–200 AD

  Roman – 200–600 AD

  The Hellenistic period was marked by its syntheses and accumulation of knowledge in certain spheres of learning, most notably by Ptolemy in astronomy, Euclid in geometry and Galen in medicine. Ptolemy gathered together existing knowledge in astronomy and, together with his own contributions to the subject, he synthesised a comprehensive new system that lasted until about 1600. We see a similar synthesis and longevity with Galen in anatomy, physiology and medicine, and with Euclid in geometry, though Euclid’s work lasted longer. The Hellenistic period saw several rival groups of philosophers vying with one another. Plato’s Academy and Aristotle’s Lyceum were still going strong, and both philosophers had their adherents. The other groups with important views about the natural world were the Epicureans and the Stoics.

  Epicurus and Epicureanism: on the Nature of Things

  Epicurus of Athens (c. 342–271 BC) was an atomist in the tradition of Leucippus and Democritus. Aristotle, as we have seen, did not believe that matter came in small, discrete particles. Epicurus believed that only atoms and the void existed. Atoms came together to form bodies, and all that we perceive (hotness, colour, etc.) could ultimately be explained in terms of the motion and the arrangement of these atoms. Aristotle had criticised Leucippus and Democritus for not distinguishing between physical indivisibility and mathematical indivisibility. However small a physical atom was, one could imagine something smaller simply by imagining something half the size. Epicurus stated very clearly that the atoms were physically indivisible but could be divided in thought into indefinitely small mathematical parts. He also placed some limits on the sizes of atoms, whereas Leucippus and Democritus had believed that they came in all shapes and sizes – though this had the unfortunate consequence of implying that there were atoms so large as to be visible. Leucippus and Democritus also believed that the world had come into being from a vortex, and that this vortex formed spontaneously. Epicurus, on the other hand, believed that all of the atoms were moving in one direction (‘down’), and on parallel paths. All atoms moved through the void at the same speed. Occasionally, an atom would swerve out of its path and so interact with other atoms. It was in this manner, Epicurus thought, that worlds began to be formed.

  The ultimate goal of the Epicureans was happiness. They rejected the view of Plato and Aristotle that one should lead a life devoted to the good, and instead aimed at pleasure. This affected the depth to which they were willing to analyse problems. Once they had an answer that they were happy with, they went no further. In some fields they went reasonably deep, while in others they barely skimmed the surface, professing themselves happy with the state of things. Epicureanism, for all its faults (and the idea of the inexplicable atomic ‘swerve’ was severely criticised, even in antiquity) was a significant trend in Hellenistic times. It was influential, too, in the Roman world – Lucretius (94–55 BC) wrote an epic poem giving an atomistic view of the world. The great problem for ancient atomic theories which relied on mechanism and chance was that they lacked the resources to produce plausible explanations of the phenomena, whether one is talking of cosmogony and cosmology or more mundane areas. They lacked any convincing account of the way in which atoms were brought together, or how they stayed together. Effectively, they were brought together by chance and stayed together by chance, hence the need of the atomists to postulate multiple worlds. The teleological accounts of Plato and Aristotle must have seemed at least as plausible at the time.

  Stoics: the Active and the Passive

  Another important school were the Stoics, whose founders were Cleanthes of Assus (331–232 BC), Chrysippus of Soli (c. 280–207 BC) and Zeno of Citium (335–263 BC) – not to be confused with Zeno of Elea. The Stoics, like the Epicureans, held that the main goal was to be happy, but they worked out an account of the cosmos that was far more detailed than anything offered by the Epicureans. Unlike them, the Stoics denied that there were atoms and a void. The cosmos was a plenum – that is, every space was filled – although the cosmos itself was situated in a void which surrounded it. The Stoics held that there were continua which could be indefinitely divided, and so there were no atoms. Like most of the
ancient Greeks, they believed that there were four elements: earth, water, air and fire. They also held that there were two fundamental principles: the active and the passive. The passive was associated with inert, quality-less matter, while the active principle, or ‘pneuma’ (breath), was associated with god. Fire was thought to be the most active element, also associated with god. It is important to stress that both of these principles were corporeal, and that they came together in what the Stoics called a ‘crasis’, or total mixture. The Stoics were therefore pantheists, since the whole of their cosmos was in a sense permeated with god, and was god.

  The Stoic account of the origin of the cosmos held that initially everything was a universal conflagration or ‘ekpyrosis’. This fire gradually changed into air, and then to the other elements. There was also supposed to be a converse process whereby the elements turned back into fire. Thus, the Stoics held a cyclical conception of the cosmos – it had no origin in the strict sense for them. In the part of each cycle in which the cosmos was coming into being from fire, it was guided by god, who retained the ‘spermatikoi logoi’, the seminal principles, through the conflagration. The Stoics disagreed with the atomists on whether the cosmos came together by chance, and their cosmos was permeated not merely by intelligence but also by providence. God had a plan for the cosmos, and it was a good plan. In these senses, the Stoics were much closer to Plato and Aristotle than to the atomists. They also held a strongly determinist view of the world. Everything that happened was pre-determined, and what is more, it would happen again in the next cycle of the cosmos. So according to the Stoics, you have already read this book in a previous cycle of the world, and you will be reading this book again in the next cycle.

  A very important idea, both in Stoic cosmology and in Western thought prior to the seventeenth century, was that of the macrocosm/microcosm relationship. This is the idea that the cosmos on a large scale – the universe – functions in the same way as, or has structural similarities to, the cosmos at small scale – human beings. So for the Stoics, the cosmos was a living creature pervaded with the active principle pneuma, and had intelligence. Each of those things could be said of the microcosm – humans – as well. This idea of an organic unity to the cosmos, a relation between the macrocosm and microcosm, was immensely important for Western thought until the scientific revolution.

  Archimedes

  Archimedes of Syracuse (287–212 BC), the son of an astronomer, provides the title for this book. It is often said that he leapt from his bath shouting ‘Eureka!’ (‘I have found it’, actually ‘heureka’ in ancient Greek), and then ran home naked, having solved a problem that was perplexing him. The problem was whether the crown of King Hieron II, supposed to be pure gold, was indeed so. It weighed the same as the gold delivered to the goldsmith, but had he adulterated the gold with silver and made a fraudulent profit with the excess? Archimedes, who had made a careful study of hydrostatics, came up with the following solution. Take an amount of pure gold equivalent in weight to the crown, and measure how much water this displaces. Do the same with silver. If the crown displaces more water than the equivalent weight of pure gold, then it has been adulterated in some way. The tale has it that Archimedes realised this while lowering himself into his bath. While this is a splendid tale, we have no proper evidence for it. There is a series of such apocryphal tales in the history of science. There is no evidence for Archimedes leaping from his bath, no evidence that Galileo dropped cannon balls from the leaning tower of Pisa (he knew of much better experiments than this already), no evidence that Newton had a realisation about gravity while sitting under an apple tree, or that Watt invented the steam engine while watching a kettle boil (the steam engine had long been invented, and Watt’s improvements to it had nothing to do with steam expanding).

  Archimedes was a brilliant mathematician and engineer. His work in geometry, his true love, developed the work of Euclid. He tended to look down on his engineering work. Cicero (106–43 BC), the Latin poet and philosopher, tells us that Archimedes refused to write any practical treatises, confining himself to theory and mathematics. Cicero also tells us that he constructed a mechanical model of the heavens which

  [W]ith a single motion reproduced all the unequal and different movements of the heavenly bodies.

  Archimedes is probably most important for his work in mechanics and in hydrostatics. He developed the theory of the lever, and formulated the principle that

  Two weights balance at distances reciprocally proportional to their magnitudes.

  He also recognised that, in principle, one could move very great weights with a relatively small force if one had a large enough lever, or a similar means of multiplying forces, and so he said:

  Give me a place to stand and I will move the world.

  It is said that Archimedes gradually pulled a large ship ashore using a system of pulleys to multiply forces, to the astonishment of those present. His study of the properties of fluids, and whether objects float, was also of great importance in antiquity. He formulated the important principle that:

  A body immersed in a liquid loses weight equal to the weight of the liquid displaced.

  There are sources which tell us that Archimedes invented the water screw, a device for raising water, and the compound pulley, a means of arranging pulleys in order to multiply force. It is unlikely that he actually originated either of these devices, but he may well have improved them and given an account of the principles involved, and how to use them in an optimum manner.

  Archimedes is said to have helped in the defence of Syracuse by inventing military engines. The most famous of these is his ‘claw’, by which it is claimed that the defenders could upend ships approaching the sea walls and sink them. Unfortunately, we do not know the nature of the claw, and can only speculate on how it worked. It is likely to have been a device whereby means for multiplying forces, such as levers and pulleys, were used to lift one end of a ship when grasped by the claw. The other end of the ship would then dip below the water, and it would sink rapidly. Archimedes died when Syracuse was finally sacked by Roman troops in 212 BC.

  Eratosthenes

  Eratosthenes of Cyrene (c. 276–195 BC) is famed for his remarkably accurate estimation of the size of the earth. He knew that at noon on the day of the summer solstice, a rod placed in the ground at Syene (near Aswan in Egypt) cast no shadow, and a well was fully illuminated at its bottom, so the sun was directly overhead. Yet a rod at Alexandria cast a shadow of 1/50 of a circle, just over 7°. A simple piece of geometry then told him that the distance between Alexandria and Syene was 7/360 of the earth’s diameter. The distance was estimated at 5,000 stades. A ‘stade’ was originally one lap of a stadium, and we believe that to have been 157.5 metres, so we get an estimate for the diameter of the earth which is 39,690 kilometres, remarkably close to the modern figure of around 40,000 km. Admittedly, we are not quite sure a rod placed in the ground at Syene (near Aswan in Egypt) cast no shadow, and a well was fully illuminated at its bottom, so the sun was directly overhead. Yet a rod at Alexandria cast a shadow of 1/50 of a circle, just over 7°. A simple piece of geometry then told him that the distance between Alexandria and Syene was 7/360 of the earth’s diameter. The distance was estimated at 5,000 stades. A ‘stade’ was originally one lap of a stadium, and we believe that to have been 157.5 metres, so we get an estimate for the diameter of the earth which is 39,690 kilometres, remarkably close to the modern figure of around 40,000 km. Admittedly, we are not quite sure how long Eratosthenes’ stade was, but even if he was using any of the other possible lengths, his calculation would still be reasonably close, within around 15 per cent. The Greeks not only knew the earth to be spherical, they also had a very good measure of its size. Eratosthenes produced very good work in geography, which was later used by Julius Caesar.

  Figure 31: Eratosthenes and the size of the earth. The angle cast by a rod at Alexandria when a rod casts no angle at Syene is equal to the angle between them, if they have the same lo
ngitude. If the distance between them is known, then one can calculate the circumference of the earth. Not to scale!

  Hero and his Engine

  One of the great inventors and technologists of later antiquity was Hero (or Heron) of Alexandria (fl. 60 AD). He did something quite remarkable. He invented a steam engine with a rotary motion 1,500 years before Watt and the industrial revolution. In all fairness, Hero’s engine was a pretty crude affair, and to construct a steam engine that would have produced any meaningful amount of power was far beyond the technological capacity of the ancients. In Hero’s engine, steam was generated in a large cauldron and then passed into a small rotating sphere with exhaust pipes pointing in opposite directions, thus generating a rotation of the sphere. The rotation was not very powerful, but there would have been movement, nonetheless. Proper steam engines actually work by another principle. If a cylinder full of steam is rapidly cooled, the steam condenses, and water and a vacuum are produced. A piston is then moved by the pressure difference between the inside of the cylinder and the outside, producing power. So Hero’s engine was a long way from a proper steam engine (and this, incidentally, is why Watt watching expanding steam from a kettle has nothing to do with his innovations).