Page:Popular Science Monthly Volume 16.djvu/267

Rh comet's tail. As I have said, Biela's comet is a case in point, and so obviously in point that it is difficult to understand how any mathematician could follow the history of the case without at once recognizing the error which nevertheless has misled and still misleads Professor Tait. That double comet, with its tails projecting from the sun, crossed the earth's path in or about the first week of September, 1872, traveling on a path slanted to the plane of the earth's orbit at an angle of twelve and a half degrees, and with a velocity considerably exceeding that of the earth in her orbit. Moving at this rate, and with this inclination, the companion comets would of course attain in ten weeks a position many millions of miles south of the plane of the earth's orbit. Thus a line from the sun to either comet would not, where prolonged into the tail, approach within many millions of miles of the earth's orbit—that is, of any position which the earth can possibly occupy. Both comets were even farther away from the actual position occupied by the earth at the time when, nevertheless, astronomers predicted a star-shower, and when, as they predicted, such a shower occurred. For the comets had left that place ten or twelve weeks before, and nearly the whole of the comets' motion had carried them away from that place, whereas only a small part of their motion had carried them away from the plane of the earth's orbit. In fact, no one who had studied with any attention the circumstances of any predicted meteor-display could have fallen into the mistake made by Professor Tait, a mistake actually so elaborated as to be made the basis of an entirely novel, and for other reasons utterly impossible, theory of comets' tails.I may here remark that the tone of the above paragraph is, in my opinion, altogether objectionable, considered in itself. It is almost impossible even for the most careful students of science to avoid making mistakes from time to time, and occasionally mistakes of the most egregious nature. There is scarcely one of the great thinkers whose work has most effectively advanced science, who has not made mistakes even in dealing with his own special subject; while those who, like the Herschels, Humboldt, and others, have dealt from time to time with subjects outside their own labors, have naturally been exposed to more serious misapprehensions. It is not wonderful that Professor Tait, engaged chiefly in analytical and physical researches, should fall into errors in dealing with astronomical matters, as when he discusses comets' tails, the solar corona, and so forth. But such errors should be corrected genially and pleasantly, not sneeringly (which, indeed, I have not done) nor censoriously. I must point out, however, that Professor Tait lays himself open to the severer forms of correction by the perfect savagery of his own corrections of mistakes made by those who chance to have offended him. The man who, in his lecture on "Force," so fiercely denounced Tyndall for mere errors, or, rather, inexactnesses of verbiage which could mislead none; the man who jeeringly exclaimed, "These be thy gods, Israel," because one of the greatest physicists of the age omitted, in defining work done in raising bodies, to mention that such bodies were on the earth, not on Jupiter or elsewhere; the man who has even honored me by his sneers at real mistakes of mine, and who with ingenious garbling has invented mistakes for me which I had never made (apparently for no other reason than because I pleasantly expostulated with him on one occasion for his attacks on Tyndall)—can hardly object to be corrected in the hard though not harsh tone adopted above. If the tu quoque defense be considered insufficient, then let me note that Professor Tait, by advancing a theory capable of being tested by evidence without being at the pains so to test it, and by refusing even to