Mathematicians Of The Day

18th September

On this day in 1846, Le Verrier wrote to Johann Galle at the Berlin Observatory asking him to look for a planet at the position he predicted. Galle located Neptune five days later. See THIS LINK.

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Quotation of the day

From Leonhard Euler
Notable enough, however, are the controversies over the series 1 - 1 + 1 - 1 + 1 - ... whose sum was given by Leibniz as 12\large\frac 1 2, although others disagree. ... Understanding of this question is to be sought in the word "sum"; this idea, if thus conceived -- namely, the sum of a series is said to be that quantity to which it is brought closer as more terms of the series are taken -- has relevance only for convergent series, and we should in general give up the idea of sum for divergent series.