## 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.

Click on Ⓟ for a poster.

##### Born:

- 1752: Adrien-Marie Legendre Ⓟ
- 1819: Léon Foucault Ⓟ
- 1863: William Metzler Ⓟ
- 1908: Victor Amazaspovich Ambartsumian Ⓟ
- 1909: Johannes Haantjes Ⓟ

##### Died:

- 1783: Leonhard Euler Ⓟ
- 1891: William Ferrel Ⓟ
- 1896: Hippolyte Fizeau Ⓟ
- 1969: Joseph Pierce Ⓟ
- 1977: Paul Bernays Ⓟ
- 2002: Siobhán Vernon Ⓟ

#### 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 $\large\frac 1 2$, 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.