the Lick Observatory makes
a very small fifth satellite not improbable.

[11] They remained there till this century. In 1835 they were quietly
dropped.

[12] It was invented by van Helmont, a Belgian chemist, who died in
1644. He suggested two names _gas_ and _blas_, and the first has
survived. Blas was, I suppose, from _blasen_, to blow, and gas seems to
be an attempt to get at the Sanskrit root underlying all such words as
_geist_.

[13] Such as this, among many others:--The duration of a flame under
different conditions is well worth determining. A spoonful of warm
spirits of wine burnt 116 pulsations. The same spoonful of spirits of
wine with addition of one-sixth saltpetre burnt 94 pulsations. With
one-sixth common salt, 83; with one-sixth gunpowder, 110; a piece of wax
in the middle of the spirit, 87; a piece of _Kieselstein_, 94; one-sixth
water, 86; and with equal parts water, only 4 pulse-beats. This, says
Liebig, is given as an example of a "_licht-bringende Versuch_."

[14] Draper, _History of Civilization in Europe_, vol. ii. p. 259.

[15] Professor Knight's series of Philosophical Classics.

[16] To explain why the entire system, horse and cart together, move
forward, the forces acting on the ground must be attended to.

[17] The distance being proportional to the _square_ of the time, see p.
82.

[18] The following letter, recently unearthed and published in _Nature_,
May 12, 1881, seems to me well worth preserving. The feeling of a
respiratory interval which it describes is familiar to students during
the too few periods of really satisfactory occupation. The early guess
concerning atmospheric electricity is typical of his extraordinary
instinct for guessing right.

"LONDON, _Dec. 15, 1716_.

"DEAR DOCTOR,--He that in ye mine of knowledge deepest diggeth, hath,
like every other miner, ye least breathing time, and must sometimes at
least come to terr. alt. for air.

"In one of these respiratory intervals I now sit down to write to you,
my friend.

"You ask me how, with so much study, I manage to retene my health. Ah,
my dear doctor, you have a better opinion of your lazy friend than he
hath of himself. Morpheous is my last companion; without 8 or 9 hours of
him yr correspondent is not worth one scavenger's peruke. My practices
did at ye first hurt my stomach, but now I eat heartily enou' as y' will
see when I come down beside you.

"I have been much amused at ye singular [Greek: _phenom