Page:Popular Science Monthly Volume 3.djvu/502

488 and 224 new groups were seen, though the sun was only observed on 196 days. The number of spots in 1870, 1871, and 1872, as well as their magnitude and duration, has been above what is usual, even at the period of maximum spot-frequency.

From all this it will be manifest that we have a well-marked peculiarity to deal with, though not one of perfect uniformity. Next to the systematic changes already considered, this alternate waxing and waning of spot-frequency might be expected to be efficient in producing recognizable weather-changes. Assuredly, if this should not appear to be the case, we should have to dismiss all idea that the sun-spots are weather-rulers.

Now, from the first discovery of spots, it was recognized that they must, in all probability, affect our weather to some degree. It was noticed, indeed, that our auroras seemed to be in some way influenced by the condition of the sun's surface, since they were observed to be more numerous when there are many spots than when there are few or none. Singularly enough, the effect of the spots on temperature was not only inquired into much later (for we owe to Cassini and Mairan the observation relating to auroras), but was expected to be of an opposite character from that which is in reality produced. Sir W. Herschel formed the opinion that, when there are most spots, the sun gives out most heat, notwithstanding the diminution of light where the spots are. He sought for evidence on this point in the price of corn in England, and it actually appeared, though by a mere coincidence, that corn had been cheapest in years of spot-frequency, a result regarded by Herschel as implying that the weather had been warmer on the whole in those years. It was well pointed out, however, by Arago, that "in these matters we must be careful how we generalize facts before we have a very considerable number of observations at our disposal." The peculiarities of weather in a single and not extensive country like England are quite insufficient to supply an answer to the wide question dealt with by Herschel. The weather statistics of many countries must be considered and compared. Moreover, very long periods of time must be dealt with.