HOOKE, ROBERT (b. Freshwater, Isle of Wight, England, 18 July 1635; d. London, England, 3 March 1702), physics.

    the celestial dynamics. In fact, his proposal did contain a revolutionary insight that reformulated the approach to circular motion in general and to celestial dynamics in particular. Notable in his statement is the absence of any reference to centrifugal force. Hooke was the man who first saw clearly the elements of orbital dynamics as we continue to accept them. If the principle of rectilinear inertia be granted, a body revolving in an orbit must be continually diverted from its inertial path by some force directed toward a center. When Hooke was formulating this view, Newton still thought of circular motion in terms of an equilibrium of centrifugal and centripetal forces. Moreover, it was Hooke who taught him to see it otherwise. Late in 1679 Hooke wrote to Newton, among other things asking for Newton's opinion of his proposed planetary dynamics. The correspondence is too well known to need repeating. Suffice it to say that in response to Newton's assumption of uniform gravity in a problem mechanically identical to orbital motion, Hooke stated his conviction that gravity decreases in power in proportion to the square of the distance. Hooke was always convinced thereafter that Newton had stolen the inverse square relation from him. Newton himself acknowledged in 1686 that the correspondence with Hooke stimulated him to demonstrate that an elliptical orbit around a central attracting body placed at one focus entails an inverse square force.

Nevertheless, one must beware of attributing too much to Hooke. Once again, his power of analysis could not support the brilliance of his insight. The insight cannot be taken from him. Where earlier investigations of the dynamics of circular motion had based themselves on the notion of centrifugal force, Hooke (as it were) stood the problem right side up and put it in a position to be attacked fruitfully. But his own mechanics was not adequate to that job. Although he proposed the problem of the dynamics of elliptical orbits, he acknowledged his inability to solve it; and his very derivation of the inverse square relation, on which he insisted with such vehemence, was so defective as to be ludicrous. He justified the inverse square relation, not by substituting the formula for centripetal force (which he appears not to have known) into Kepler's third law, but by a bastardized application of his own general rule of mechanics to Kepler's aborted law of velocities. Hooke did not discover or even approach the law of universal gravitation. But he did set Newton on the correct approach to orbital dynamics and, in this way, contributed immensely to Newton's later triumph.

Although one important area of Hooke's scientific activity, his study of fossils and his related contribution to geology, also figured in the Micrographia, its major exposition appeared only in the “Lectures and Discourses of Earthquakes,” the largest section of his Posthumous Works. Spread over a period of thirty years, the lectures testify that geology was one of Hooke's enduring interests. Geology might almost have been created to display his talents to maximum advantage. An almost untouched field, it presented no massive volume of data to be mastered and offered few constraints to curb his facile imagination. Hooke repaid it handsomely. He provided a solution to the controversy over the origin of fossils by dividing “figured stones” into two categories—those with forms characteristic of the organism and those with forms characteristic of the substance. In regard to the latter, Hooke may be described as a protocrystallographer. He showed how the polyhedral forms of crystals (as he saw them under the microscope) could be built up from packings of bullets, the basis for the claim that he anticipated Steno in the law of constancy of interfacial angles.

In an age when the biblical account of creation made fossils with organic forms a riddle to most investigators, Hooke was remarkable for his steadfast refusal to consider them as anything but the remains of organic creatures. His refutation of the argument that they are lusus naturae, sports of nature produced to no purpose, is one of the classic passages of scientific argumentation in the seventeenth century. He refused to call in the Deluge to explain the presence of marine fossils far from the sea, but he concluded that the surface of the earth has been subject to vast upheavals and changes. When fossils could not be identified with existing creatures, he did not hesitate to consider the mutability of species.

One must be careful not to exaggerate the modernity of Hooke's geological ideas. Unable to destroy the preconception of a limited time span, he identified the upheavals of the surface of the earth with cataclysmic earthquakes. He has been called the first uniformitarian; quite the contrary, he was the first catastrophist. The mutations of species he conceived were limited variations under the stress of environmental change. To say as much is only to concede that Hooke could not leap from the seventeenth century into the nineteenth. With the possible exception of Steno, he was easily the most important geologist of his day. In nothing does he appear more modern than in his prescription of a program for geological study. Fossils are the “Monuments” and “Medals” of earlier ages from which the history of the earth can be reconstructed, just as the history of mankind