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Rh has gone on at least during the last century and a half. Before that the records are too scanty to give us full or trustworthy information: people did not pay enough attention to the Sun.

We must not be too ready to blame them because we ourselves do not pay nearly enough attention to him even now, considering his immense importance to us. Up till a year or two ago, no one had ever taken the trouble to make sure whether light and heat came to us from the Sun with strict regularity, or whether they vary in amount as the spots do. It has been calmly assumed that we can depend on