y and mathematics at Glasgow, and was one of
the first to use the barometer in measuring altitudes. The work to which De
Morgan refers is his _Hydrostaticks_ (1672). He was a firm believer in evil
spirits, his work on the subject going through four editions: _Satan's
Invisible World Discovered; or, a choice collection of modern relations,
proving evidently against the Saducees and Athiests of this present age,
that there are Devils, Spirits, Witches, and Apparitions_, Edinburgh, 1685.

[472] This was probably William Sanders, Regent of St. Leonard's College,
whose _Theses philosophicae_ appeared in 1674, and whose _Elementa
geometriae_ came out a dozen years later.

[473] _Ars nova et magna gravitatis et levitatis; sive dialogorum
philosophicorum libri sex de aeris vera ac reali gravitate_, Rotterdam,
1669, 4to.

[474] Volume I, Nos. 1 and 2, appeared in 1803.

[475] His daughter, Mrs. De Morgan, says in her _Memoir_ of her husband:
"My father had been second wrangler in a year in which the two highest were
close together, and was, as his son-in-law afterwards described him, an
exceedingly clear thinker. It is possible, as Mr. De Morgan said, that this
mental clearness and directness may have caused his mathematical heresy,
the rejection of the use of negative quantities in algebraical operations;
and it is probable that he thus deprived himself of an instrument of work,
the use of which might have led him to greater eminence in the higher
branches." _Memoir of Augustus De Morgan_, London, 1882, p. 19.

[476] "If it is not true it is a good invention." A well-known Italian
proverb.

[477] See page 86, note 132.

[478] He was born at Paris in 1713, and died there in 1765.

[479] _Recherches sur les courbes a double courbure_, Paris, 1731. Clairaut
was then only eighteen, and was in the same year made a member of the
Academie des sciences. His _Elemens de geometrie_ appeared in 1741.
Meantime he had taken part in the measurement of a degree in Lapland
(1736-1737). His _Traite de la figure de la terre_ was published in 1741.
The Academy of St. Petersburg awarded him a prize for his _Theorie de la
lune_ (1750). His various works on comets are well known, particularly his
_Theorie du mouvement des cometes_ (1760) in which he applied the "problem
of three bodies" to Halley's comet as retarded by Jupiter and Saturn.

[480] Joseph Privat, Abbe de Molieres (1677-1742), was a priest of the
Congregation of the Oratorium.