Page:Popular Science Monthly Volume 66.djvu/515

Rh meteorological records, only those will be taken in which some possible relation to the sunspot periods may exist. Thus a search is to be made for 11-year periods to establish a good connection; the 35-year period may furnish a possible connection between the two sets of phenomena, although, as we have seen, its existence in the sunspot curves is too doubtful to demonstrate the existence of the connection, while the 55 to 65-year periods, even if they exist in the sunspot curves, are too long to make a demonstration possible within the range of the recorded meteorological observations.

The best proof of the existence of an 11-year period has been furnished by Köppen, who showed that there was such a cycle in the combined mean annual temperature of many places within the tropics. But the total range of variation is only about three-quarters of a degree, while the mean annual temperatures show variations of from five to ten degrees. This appears to be the only well-established quantitative result with respect to the 11-year period. But several qualitative examinations have been made and the recent ones chiefly refer to rainfall and famine in India. Sir Norman and Dr. W. J. S. Lockyer have examined the rainfall statistics in India and Mauritius and they come to the conclusion that India has an increased rainfall near the sunspot maximum and Mauritius one near the sunspot minimum, and further, that the latter gives rise to a smaller pulse of rainfall in India. Thus India has two periods of increased rainfall, a large one near the sunspot maximum and a smaller one near the sunspot minimum. Unfortunately this investigation only refers to a single period of eleven years—from 1877 to 1886. They have also brought forward some evidence which indicates that the famine years occur between these two pulses of rainfall. The results do not seem to be sufficiently well made out to prophesy future famines with any certainty. Last year another writer showed a connection between certain Greenwich temperature records and the 11-year period, but the differences shown were very small. Other investigations on the same lines indicate about the same or a less degree of success in the discovery of a sunspot period.

In view of the doubtful existence of a 35-year period in the solar activity it is unnecessary to say much concerning a similar period in terrestrial phenomena. The most thorough investigation is that of Brückner, who examined a very large number of temperature records from all parts of the earth and deduced from the annual means a period of this length. But the amount of the change is only half a degree Fahrenheit, while the annual averages differ amongst themselves by from 5° to 10°.

In summing up briefly the results of the evidence hitherto presented, it must be admitted that no case has been made out in favor of a