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cerns. True, practitioners were wont likewise to take their point of departure in some ancient text. Vesalius started from Galen; Brunfels from Dioskorides; Nunes from Ptolemy; many a collecting naturalist from Pliny; Agrippa from legendary ‘Hermes’; many an applied math- ematician from the legendary Archimedes and the military feats ascribed to him of old. However, time and again events branched out from there in empiricist, forward-looking directions quite different from the efforts at reconstruction of ancient wisdom undertaken at the time by the philosophers and the mathematicians. Broadly speaking, the recovery and enrichment of Greek mathematical science were the concern of humanists enjoying court patronage, and the cultivation of natural philosophy was overwhelmingly an affair of university-seated scholastics. The empiricist search to enhance factual knowledge of the natural world and gain some measure of control over it, while enjoying court patronage more often than not, was carried out as a rule by scholars connected to the world of the arts and crafts. So the unmistakable lack of interaction between the three modes of nature- knowledge simultaneously present in Renaissance Europe (the two culture-transcending, Greek modes and the culture-bound, European mode) was furthered by the different social positions practitioners occupied. It was not, however, uniquely caused thereby. A suitable way to demonstrate that it was not is to consider the exceptional case of a man who took an active part in both the Athenian and the ‘European’ modes of nature-knowledge while characteristically managing to keep the two separated in his own head.
That man was a Portuguese scholar by the name of João de Castro. I use his case for another purpose as well – his achievement points at a significant potentiality inherent in Europe’s control-oriented empiricism. As we saw earlier in the case of Leonardo, accurate, action-directed observation might on occasion consolidate into more narrowly targeted ranges of deliberate experimentation. It was not that the act of experiment was so novel per se – recall Pythagoras’ consonance-producing monochord, Ibn al-Haytham’s oil-lamp shining through a tube, Pierre de Maricourt’s bisected yet still bipolar magnets, or all kinds of operations tried out over the centuries in alchemy. Truly new was experiments being carried out, not incidentally as before, but in well thought-out, progressive series. That is what, hidden from the world, Leonardo was occupied with: he was systematically setting up a coherent range of experiments to find out how materials behave under deliberately varied conditions of friction. In his own manner, Castro did similar things.
Around 1538, at the age of thirty-eight, he wrote Tratado da esfera – one of numerous cosmological treatises produced between the early 13th and the 17th century on the model of Sacrobosco’s De sphaera (p. 82). Here Castro stuck to Aristotelian doctrine in its most orthodox variety, but for one peripheral exception. When treating Aristotelian themes like the allegedly small amount of dry land in proportion to the Earth’s waters, he marked his disagreement by pointing at contrary evidence obtained by his countrymen in their mari- time probings to the south and east. Castro was deeply engaged in these overseas adventures
140 himself – he ended his career as viceroy of India from 1545 until his early death in 1548. Ex- cept for these few passages, however, nothing in the Tratado reflects the experience.
Little as Portugal’s incipient empire building was able to direct Castro’s mind in its Athe- nian mode, so much the more did it affect that same mind when engaged in writing up, between 1538 and 1541, the three consecutive Roteiros (travel reports) he kept on board ship from Lisbon to Goa, from Goa to Diu, and from Goa to Suez. In these notes a quite different spirit prevails – the coercively empiricist spirit of nature-knowledge colored the European way.
King João III charged Castro with making observations on the behavior of sea-water and magnets. The Roteiros display an unceasing, methodically exercised interest in both the unknown and the allegedly known. Castro gave a detailed eyewitness account of a basalt formation on the southwest coast of India. He interrogated Ethiopian chieftains to cor- rect Pliny’s tales about the sources of the Nile. He was on the lookout all the time for novel facts and described them in much accurate detail without any effort to squeeze them into philosophically prestructured categories. More often than not, Castro collected evidence with some assumed natural regularity in mind. A systematically executed series of compass readings convinced him of the untenability of the widespread conviction that there must be a ‘true meridian’ of variation zero in respect to the magnetic pole. More than half a century later a man of the stature of Simon Stevin would still erect his Havenvinding (The Haven- Finding Art) upon that hoped-for resolution of the problem of geographical longitude.
When facing new facts, Castro felt a persistent need to check their truth against the two sources of possible error he in effect identified: those arising from human fallibility and those that might flow from instrumental design and operation. He subjected his astrolabes and compasses to critical scrutiny. Anyone who happened to be around might be recruited to serve as a witness or to assist in the repetition of an observation. On one occasion
Castro found a latitude of 160, the contramestre 17 1/30, a mariner 17 1/30 and the caulker – “a practical man of great experience” [“homem practico experimentado”] – 16 1/40.82
Not until Castro had found that an observed yet incongruous fact withstood all serious criticism and had to be accepted as genuine did he seek for possible causes in unforeseen influences arising from some stuff or event nearby. That way “Castro [became] the first to discover that the capricious behaviour of the needle on board of a ship may be caused by iron objects.”83 More often than not, however, he was unable to identify such an element in
the environment with sufficient plausibility. In such cases he consistently refused to take the customary way out, which was just to dream up some explanation. Instead, he left the solu- tion to the admired Pedro Nunes, who had taught him the theory and practice of marine instruments, or he resorted to his pet phrase ‘let Apollo solve it’.
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Near coincident with Castro’s death in 1548, the Portuguese, albeit the very people to set out on the discovery, exploration, and exploitation of foreign lands and their inhabitants, began to drop out of the further pursuit of the kind of nature-knowledge that went with these activities. The Spanish soon proved subject to this early case of ‘imperial overstretch’, too. Around 1600 other seafaring nations, notably the British and the Dutch, began to contribute to the advance of nature-knowledge of a descriptive, practice-oriented, and – in ways first explored by Leonardo and by Castro – occasionally experimental kind.