Page:Popular Science Monthly Volume 3.djvu/504

490 between them. Nevertheless, I would not urge this with the desire of in any way throwing doubt upon the opinion to which Prof. Smyth has been led, knowing well that the long and careful examination he has given to this subject in all its details may have afforded ample though not obvious evidence for the conclusions at which he has arrived. I note, also, that, as he points out, Mr. Stone, director of the Cape Town Observatory, and Mr. Cleveland Abbe, director of the Cincinnati Observatory, have since, "but it is believed quite independently, published similar deductions touching the earth's temperature in reference to sun-spots." All I would remark is, that the effect is very slight, and very far from being obvious at a first inspection.

Next as to rainfall and wind.

Here, again, we have results which can hardly be regarded as striking, except in the forcible evidence they convey of the insignificance of the effects which are to be imputed to the great eleven-year spot period. We owe to Mr. Baxendell, of Manchester, the most complete series of investigations into this subject. He finds that, at Oxford, during the years when sun-spots were most numerous, the amount of rainfall under west and southwest winds was greater than the amount under south and southeast winds; while the reverse was the case in years when spots were few and small. Applying corresponding processes to the meteorological records for St. Petersburg, he finds that a contrary state of things prevailed there. Next we have the evidence of the Rev. R. Main, director of the Radcliffe Observatory at Oxford, who finds that westerly winds are slightly more common when sun-spots are numerous than at other times. And, lastly, Mr. Meldrum, of Mauritius, notes that years of spot-frequency are characterized, on the whole, by a greater number of storms and hurricanes than years when the sun shows few spots.

The association between the sun-spot period and terrestrial magnetism is of a far more marked character, though I must premise that the Astronomer Royal, after careful analysis of the Greenwich magnetic records, denies the existence of any such association whatever. There is, however, a balance of evidence in its favor. It seems very nearly demonstrated that the daily sway of the magnetic needle is greatest when sun-spots are numerous, that magnetic storms are somewhat more numerous at such times, and that auroras are also more commonly seen. Now, it has been almost demonstrated by M. Marié Davy, chief of the meteorological division in the Paris Observatory, that the weather is affected in a general way by magnetic disturbances. So that we are confirmed in the opinion that, indirectly, if not directly, the weather is affected to some slight degree by the great sun-spot period.

Still, I must point out that not one of these cases of agreement has any thing like the evidence in its favor which had been found for an association between the varying distance of Jupiter and the sun-spot changes. For eight consecutive maxima and minima this association