Ernest William Brown

“ In dealing with any complicated problem it is usually best to try and simplify it as much as possible, and if the problem even then appears too difficult, to attack a special case, and this is undoubtedly the best plan to pursue here. In order to avoid the rapid fluctuations which occur in the temperate zones, meteorologists have turned to places in the tropics where the types of weather during the course of a year are apt to be much more permanent and where the changes from one year to another are likely to appear more clearly than in other regions of the earth. ”

“ Although a negative answer must at present be given to the question whether sunspots have any considerable share in the variations of climate, it would be leaving a wrong impression if no mention were made of a well-established 11-year period in the variations of another set of terrestrial phenomena. The state of the earth's magnetism has for many years been carefully recorded by suitable instruments and there is no doubt that its fluctuations correspond quite closely with the state of the sun's surface, not only in the cycle of long period, but also with respect to the minor variations. ”

“ 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. ”

“ 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. ”

“ In countries where the most important interests are manufacturing and ocean transportation, the 'weather' is the first consideration; in lands where the agricultural interests are predominant, although the weather is important, it is more essential to have an idea of the climatic or seasonal changes. Thus if the sunspot period could be shown to have a large influence on the climate of any region, we should be able to forecast to a corresponding extent the general characteristics of future seasons, and lay plans accordingly. ”

“ For example, an increase of heat from the sun may produce increased evaporation from certain water areas of the earth's surface, and the moisture thus drawn up being carried away by the movements of the atmosphere, may be deposited elsewhere in the form of snow or rain. It is almost impossible without a much more intimate knowledge of the laws governing the movements in our atmosphere to say in advance what the effect of a slow and periodic change in the sun's heat will be. ”

“ Whatever other causes operate, there can be little doubt that the sun must play some part in governing the climate of any particular place. The day and the year are therefore marked out beforehand as periods into which observations of temperature can be grouped, and these periods are fully confirmed. ”

“ The time of revolution of the moon, under the supposition that the moon has any influence, is not found in meteorological observations, or at any rate the effect is so small as to be negligible in comparison with what we want to find, and no other astronomical period seems very likely to find a counterpart in the records. There is, however, one period which at first sight appears to be a possible one in meteorological observations, namely, that known as the sunspot period. ”

“ The long period changes are in general those which affect the character of a season and which show the difference between one season and the next, or the variations which a given season of the year will show in several successive years. ”

“ It seems to be generally agreed that, owing to its political and geographical situation, India is the country best fitted to satisfy these various conditions. The most marked peculiarity of its climate, taking the country as a whole, is a rainy season extending over some two or three months, with comparatively little precipitation per month during the rest of the year. ”

“ 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. ”

“ If the temperatures be recorded every hour out of the twenty-four for a large number of days, and the average temperature for each hour be formed by adding all the observations for that hour and dividing by the number of them, we obtain a series of twenty-four average temperatures. When the number of days on which observations are recorded is great enough, these averages will show a regular change rising to a maximum, for most places, in the early afternoon and descending to a minimum in the early morning hours. ”

“ The average period between the minima or dates of fewest sunspots is rather less irregular, since it has never been known to differ by much more than two years from the mean period of 11 years. There is some evidence that these stronger and weaker maxima themselves run in a cycle, but the period is very doubtful. Wolf, who devoted most of his life to the investigation of sunspots, deduced a period of 55 years for this longer cycle, while there are later determinations of 60, 351/2 and 61 years. ”

“ It is only successful in the few cases where the general nature of a group appears without much trouble. The second method is to assume that the observations must run in series which are repeated after definite intervals of time. These intervals of time are in reality obtained from the general physical principle that if any force is periodic, that is, if its fluctuations are repeated after a definite period of time, then certain of its effects are also repeated after a definite period of time, which is the same as that of the force. ”

“ There is good reason to believe that a period of about 35 years is to be traced in certain of the meteorological records, and therefore it is important to know how much dependence can be placed on the evidence for the existence of a similar period in the sunspot observations. ”

“ In the second place, the observations at one place should be kept separate from those at other places, for it is theoretically possible and even probable that a maximum at one place of observation may occur at the same time as a minimum at another place. ”

“ It is evident then that other cycles must be sought which, by their combined effect, will give the actual temperature at any particular time. And what has been said about temperature can be said to a greater or less degree about the other phenomena, such as rainfall or barometric pressure, which it has been customary to record. We find periods of a day and a year, but the differences of the averages from the actual observations are very considerable. ”

“ Second, the meteorological records over long intervals of time must be examined in order to see whether they exhibit similar cycles of change and whether those cycles, supposing that they exist, are sufficiently well-marked to be considered important factors in the variations of the seasons at any place from year to year. ”

“ Thus we have a well-marked average period of about 11 years and doubtful ones of about 35 and 60 years. These are therefore the periods into which the meteorological records are to be grouped in order to inquire whether there is any connection between the two sets of phenomena. ”