As _light_ may be produced by other methods than have been yet described, as from _rotten wood_, _fish_, _meat_ &c. I shall endeavour to give an account, how, and in what manner, that _light_ is produced. Mr. _Boyle_ (in vol. 2. p. 233. of the epitome by _Boulton_) tells us, that by putting _rotten wood_, _fish_, _flesh_ &c. in the receiver of an air-pump, and then extracting the gross air, they all, in a little time, lost their _shining_ or _luminous_ quality; but, upon a re-admission of air, this _luminous_ quality returned. From which we may learn, that the air is essentially necessary to continue this _light_; and, of consequence, that this _light_ is produced by the _action_ and _re-action_ of the air on the body, which cause an _intestine motion_ of its parts; and thereby the emission of the said light; for when any thing begins to ferment and _putrify_ (which cannot be performed in any place, but where the gross air is present) the _intestine motion_ of its parts is thereby _increased_; which _motion_ acting upon the air pressed into it, the air is thereby _ground_ very small, and by the continual pressure of the atmosphere is sent out so small, as to be in form of _light_.--In the common _fermentation_ of liquids, when it rises to any height, those particles of _light_ being _stopped_, and _entangled_ by the _watry parts_ of the fermenting mass, thereby produce _heat_; and some mixtures will produce _light_, _heat_ and _flame_ on fermentation; as _steel_, _water_, and _sulphur_. By these experiments we have a clear idea of the means and method by which _fermentation_ is performed, which operation has been hitherto unintelligible. From hence we may likewise see the reason why, in an air either _too hot_ or _too cold_, _fermentation_ cannot be performed; for in an air _too cold_, the pressure is _too great_, and also the grains of air _too large_ to _enter_ and _divide_ the thing to be _fermented_; by which means the _motion_ of its parts requisite to _fermentation_ is prevented; but in air that is _too hot_, there must be just the contrary effect, for there the parts of the thing to be _fermented_ are so far _expanded_, and the air so _rarified_, as to pass through the body with little or no obstruction, and of consequence to produce little or no _intestine motion_ of its parts; and that there is in _fermentations an intestine motion_ of the parts of a _fermenting_ liquid, is easily discernible by the naked eye. This also gives us the reason, why the _glow-worm_ shines only in the summer months, when the air is greatly _rarified_, or _divided_, and then requires but a small _motion_ to give it the form of _light_.