degrees express. If the sunbeams were totally intercepted, so that the earth derived no heat whatever from this source, the temperature of our globe would fall not merely to zero, but it must sink down to a point far below zero, even to the temperature of space itself; what this may be is a matter of some uncertainty, but from all the evidence attainable it seems plain that we may put it at not less than 300° below zero. It therefore follows that at the time of the heat-wave, when the thermometer indicated 100°, the sun's beams actually maintained the affected region of the earth at 400° above what it would have been if the sun were absent. This will show us that the heat- wave was not after all such a very exceptional matter so far as the sun was concerned. Had the temperature been only 80° at New York we should never have heard of the sun-strokes and all the other troubles; it was the extra 20° which made all the difference—in other words, so long as the sun merely kept the earth about 380° above the temperature of space no one thought anything about it, but the moment it rose to 400° it was expected that something tremendous must have happened. This way of looking at the matter places the great heat-wave in its proper cosmical perspective; it was no such great affair after all; it merely meant a trifling addition of 5 per cent, to the temperature usual at that season—that is to say, when the temperature is measured in its proper way. This shows us that a very trifling proportional variation in the intensity of the sun's radiation might be competent to produce great climatic changes. It seems hardly possible to doubt that if, from any cause, the sun shed a small percentage of heat more than it was wont to do, quite disproportionate climatic disturbances would be the result.
