162 HISTORY OF THE [1860-70 In the same month, Schiaparelli had from his own calculations of the meteoric orbit made the same comparison. Yet again in February, Le Verrier, noting Peters's suggestion, had recalculated the meteoric orbit, utilising A. S. HerschePs determination of the radiant in 1866, and had found a better agreement with Oppolzer's orbit. And in 1867 March, Adams had completed the calculations of the planetary perturbations, and had found that the observed variation of the node of the meteoric orbit could not be reconciled with the four shorter periods indicated by H. A. Newton, but was completely satisfied by the longest period. From a combination of five new determinations of the radiant with that derived from his own observations with an instrument specially devised by him, he deduced a definitive orbit still more closely in agreement with Oppolzer's orbit for Tempel's comet (MJV., 27, 247). And thus was established the close relation between comets and meteors. Pritchard's second Presidential Address was delivered in 1868, on the occasion of the award of the Gold Medal to Le Verrier, for his theories and tables of the four planets, Mercury, Venus, Earth. Mars. It was with this work that Pritchard dealt in his address. For his later work on the theories of Jupiter, Saturn, Uranus, and Neptune, the medal was again awarded to Le Verrier in 1876, and on that occasion Adams delivered the address. The earlier work led Le Verrier to infer that there existed on the one hand in the neighbourhood of Mercury, and on the other hand in the neighbourhood of Mars, sensible quantities of matter, the action of which had not been taken into account. In the case of Mars, the mass of the earth itself was at fault ; it had been assumed too small, having been derived from too small a value of the solar parallax. " With respect to Mercury, a similar verification has not yet taken place, but the theory of the planet has been estab- lished with so much care, and the transits of the planet across the sun furnish such accurate observations as to leave no doubt of the reality of the phenomenon in question ; and the only way of accounting for it appears to be to suppose, with M. Le Verrier, the existence of several minute planets, or of a certain quantity of diffused matter circulating about the sun within the orbit of Mercury " (Adams, M.N., 36, 232). Considerations like these, set forth by men like Le Verrier and Adams, even though half a century ago, still carry weight with those who hesitate to accept the astronomical evidence of the deflection of light in a gravitational field as a crucial verification of the truth of Einstein's theory ; to them the astronomical evidence
