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pect a want of uniformity in the proper mo-
tion of Sirius and Procyon respectively. In
1844, in a letter to Sir John Herschel,[15] he
attributed these irregularities in each case
to the attraction of an invisible compan-
ion, the period of revolution of Sirius be-
ing about half a century. Later he said: ”I
adhere to the conviction that Procyon and
Sirius form real binary systems, consisting
607
