Every one made mistakes.
Thus, it is a most remarkable feature of the discovery of Neptune that mistakes were made by almost every one concerned, however eminent. Airy made a mistake in regarding the question of the Radius Vector as of fundamental importance; Sir J. Herschel was wrong in describing an elementary method which he considered might have found the planet; Professor Peirce was wrong in supposing that the actual and the supposed planet were essentially different in their action on Uranus; Le Verrier was wrong in assigning limits outside which it was not necessary to look when the actual planet was outside them; Adams was more or less wrong in thinking that the eccentricity of the new planet could be found from the material already at disposal of man. Both Adams and Le Verrier gave far too much importance to Bode’s Law.
To review a piece of history of this kind and note the mistakes of such men is certainly comforting, and need not in any way lessen our admiration. In the case of the investigators themselves, much may be set down to excitement in the presence of a possible discovery. Professor Sampson has provided us with a small but typical instance of this fact. When Adams had carried through all his computations for finding Neptune, and was approaching the actual place of the planet, he, “who could carry through fabulous computations without error,” for the first time wrote down a wrong figure. The mistake was corrected upon the MS., “probably as soon as made,” but no doubt betrays the excitement which the great worker could not repress at this critical moment. There is a tradition that, similarly, when the mighty Newton was approaching the completion of his calculations to verify the Law of Gravitation, his excitement was so great that he was compelled to assign to a friend the task of finishing them.
Finally, we may remark how the history of the discovery of Neptune again illustrates the difficulty of formulating any general principles for guiding scientific work. Sometimes it is well to follow the slightest clue, however imperfectly understood; at other times we shall do better to refuse such guidance. Bode’s Law pointed to the existence of minor planets, and might conceivably have helped in finding Uranus: but by trusting to it in the case of Neptune, the investigators were perilously near going astray. Sometimes it is better to follow resolutely the work in hand whatever it may be, shutting one’s ears to other calls; but Airy and Challis lost their opportunities by just this course of action. The history of science is full of such contradictory experiences; and the only safe conclusion seems to be that there are no general rules of conduct for discovery.
CHAPTER III
BRADLEY’S DISCOVERIES OF THE ABERRATION OF LIGHT AND OF THE NUTATION OF THE EARTH’S AXIS
Biographical method adopted.
In examining different types of astronomical discovery, we shall find certain advantages in varying to some extent the method of presentation. In the two previous chapters our opportunities for learning anything of the life and character of those who made the discoveries have been slight; but I propose to adopt a more directly biographical method in dealing with Bradley’s discoveries, which are so bound up with the simple earnestness of his character that we could scarcely appreciate their essential features properly without some biographical study. But the record of his life apart from his astronomical work is not in any way sensational; indeed it is singularly devoid of incident. He had not even a scientific quarrel. There was scarcely a man of science of that period who had not at least one violent quarrel with some one, save only Bradley, whose gentle nature seems to have kept him clear of them all. Judged by ordinary standards his life was uneventful: and yet it may be doubted whether, to him who lived it, that life contained one dull moment. Incident came for him in his scientific work: in the preparation of apparatus, the making of observations, above all in the hard-thinking which he did to get at the clue which would explain them; and after reviewing his biography,[2] I think we shall be inclined to admit that if ever there was a happy life, albeit one of unremitting toil, it was that of James Bradley.