It is somewhat in this manner that we must seek to explain what is called the great heat-wave. The temperature at any place has of course the main annual period corresponding to the variation with the seasons, but there are many other periodic fluctuations in the temperature analogous to those minor tides to which we have already referred. Generally speaking, of course, these will not all conspire; some will be tending to elevate the temperature and others to depress it at any time. It is the net result of all that we actually perceive. Sometimes, however, it will happen that several of these, or at all events some of the more important ones, move in the same direction; then of course we have great exaltation of temperature such as that which the newspapers have called the great heat-wave.
It is, however, quite possible that certain changes in progress on the sun may act in a specific manner on our climate. I do not indeed say that there is much reason for thinking that the great heat-wave has really been connected with any intrinsic changes in our luminary, but it is just possible that something of the kind may have occurred. I would consequently like to devote some little space to the consideration of this interesting subject.
In the discussion of such a question there is a fundamental point which must always be borne in mind. We must remember the full extent of the earth's indebtedness to sunbeams. We have spoken of a temperature of 100° during the continuance of the great heat-wave, and it is necessary to understand all that this implies. Of course, on our thermometric scale a temperature such as we have mentioned merely means 100° above a certain arbitrary zero, but the sun has sent us more heat than those hundred
