has been strongly marked, and might be viewed as demonstrated—only it chances, unfortunately, that, for two other cases, the relation is precisely reversed; and, in point of fact, whereas the period now assigned to the great sun-spot wave is eleven years and rather less than one month, Jupiter's period of revolution is eleven years and about ten months, a discrepancy of nine months, which would amount to five and a half years (or modify perfect agreement into perfect disagreement) in seven or eight cycles.
But, accepting the association between weather and the sun-spot changes as demonstrated (which is granting a great deal to the believers in solar weather-prediction), have we any reason to believe that by a long-continued study of the sun the great problem of foretelling the weather can be solved? This question, as I have already pointed out, must not be hastily answered. It is one of national, nay, of cosmopolitan importance. If answered in the affirmative, there is scarcely any expense which would be too great for the work suggested; but all the more careful must we be not to answer it in the affirmative, if the true answer should be negative.
But it appears to me that so soon as the considerations dealt with above have been fairly taken into account, there can be no possible doubt or difficulty in replying to the question. The matter has, in effect, though not in intention, been tested experimentally, and the experiments, when carried out under the most favorable conditions, have altogether failed. To show that this is so, I take the position of affairs before Schwabe began that fine series of observations which ended in the discovery of the great spot-period of eleven years. Let us suppose that at that time the question had been mooted whether it might not be possible, by a careful study of the sun, to obtain some means of predicting the weather. The argument would then have run as follows: "The sun is the great source of light and heat; that orb is liable to changes which must in all probability affect the supply of light and heat; those changes may be periodical, and so predictable; and, as our weather must to some extent depend on the supply of light and heat, we may thus find a means of predicting weather-changes." The inquiry might then have been undertaken, and undoubtedly the great spot-period would have been detected, and with this discovery would have come that partial power of predicting the sun's condition which we now possess—that is, the power of saying that in such and such a year, taken as a whole, spots will be numerous or the reverse. Moreover, meteorological observations conducted simultaneously would have shown that, as the original argument supposed, the quantity of heat supplied by the sun varies to a slight degree with the varying condition of the sun. Corresponding magnetic changes would be detected; and also those partial indications of a connection between phenomena of wind and rain and the sun's condition which have been indicated above. All this would be exceedingly interesting to men of
