See _ante_, ii.403, and iii.352.
[737] See _ante_, iii.398, note 3.
[738] 'Sept. 22, 1783. The chymical philosophers have discovered a body
(which I have forgotten, but will enquire) which, dissolved by an acid,
emits a vapour lighter than the atmospherical air. This vapour is
caught, among other means, by tying a bladder compressed upon the body
in which the dissolution is performed; the vapour rising swells the
bladder and fills it. _Piozzi Letters_, ii.310. The 'body' was
iron-filings, the acid sulphuric acid, and the vapour nitrogen. The
other 'new kinds of air' were the gases discovered by Priestley.
[739] I do not wonder at Johnson's displeasure when the name of Dr.
Priestley was mentioned; for I know no writer who has been suffered to
publish more pernicious doctrines. I shall instance only three. First,
_Materialism_; by which _mind_ is denied to human nature; which, if
believed, must deprive us of every elevated principle. Secondly,
_Necessity_; or the doctrine that every action, whether good or bad, is
included in an unchangeable and unavoidable system; a notion utterly
subversive of moral government.
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