Page:Popular Science Monthly Volume 66.djvu/517

Rh do the variations of the sunspot records. As yet, the number of years in which a continuous account of the prominences has been kept is too small to establish any good connection with the long-period or climatic changes on the earth's surface. It was only in 1868 that Lockyer and Janssen devised a method of observing them at times other than those rare ones when the moon comes in front of the sun's disc and leaves anything protruding from the edge of the latter in plain view for a few seconds. In general, large and numerous prominences are associated with the presence of sunspots, but prominences are frequently observed when no sunspots are visible in their neighborhood.

While this new method of noting the prominences in preference to the sunspots will probably improve our knowledge of what is going on in the sun, there is some tendency towards a change in the methods of observing the terrestrial atmosphere. The possibility of obtaining observations at heights of 2,000 feet or more above the earth's surface has directed attention to the fact that we are much more likely to get results free from local influences in this way, and perhaps a continuous series of such observations may show better any regular changes in the atmospheric phenomena. At the same time, the opinion has been strongly expressed that the observations already at hand should be sufficient to give the main features of the weather and climate if they can tell anything at all, and that it is time to stop the huge accumulation of records of temperature, rainfall, etc., and to undertake the thorough examination of those in our possession. There is undoubtedly great need for this: a plenteous harvest, with perhaps many tares and but few laborers.

In conclusion, while it is not my purpose to go into the reasons why more or fewer sunspots and prominences should affect our atmosphere, a few words may be said on the subject in order to counteract a widely spread misconception. Because the sunspots are dark areas, it is supposed—and one sees the statement frequently in the popular prints—that a portion of the sun's heat is screened off and the immediate deduction is made that 'cold waves' are the result. The first idea is very probably the exact opposite of the truth, and there is no theoretical or observed foundation for the second. As a matter of fact, it is generally agreed that sunspots and the associated prominences are evidences of increased activity, and therefore that they should denote a greater instead of a less output of solar heat. The amount of the change in the solar heat from time to time is as yet unknown; investigations in this direction are only in their infancy. Moreover, it is probable that the changes are too small to very materially affect terrestrial conditions, and even if they do so, the nature of the effect is quite doubtful. For example, an increase of heat from the sun may produce increased evaporation from certain water areas of the earth's