Boyle proved that light from the wood was able to pass a vacuum and later showed that "shining fish" behaved as the "shining wood," but that a piece of white hot iron would not regain its light on readmitting air to the exhausted receiver and that the iron lost its glow under the air-pump merely because it cooled off. A piece of glowing coal, however, did lose its light in the absence of air and regained it on again admitting air, provided the air had not been removed for too long. Boyle was apparently impressed with the similarity of the light giving process in glowing coal and shining wood as he draws a comparison between the two which brings out the fundamental similarity of combustion processes. "Resemblances: VII. The Things wherein I observed a Piece of _shining Wood_ and a _burning Coal_ to agree or _resemble_ each other are principally these _five_: 1. Both of them are _Luminaries_, that is, give _Light_, as having it (if I may so speak) _residing in them_; and not like _Looking-glasses_, or _white Bodies_, which are conspicuous only by the _incident Beams_ of the _Sun_, or some other _luminous Body_, which they _reflect_.... 2. Both _shining Wood_ and a _burning Coal_ need the Presence of the Air (and that too of such a _Density_ to make them continue _shining_).... 3. Both _shining Wood_ and a _burning Coal_, having been deprived, for a Time, of their _Light_, by the withdrawing of the contiguous _Air_, may presently recover it by letting in fresh _Air_ upon them.... 4. Both a _quick Coal_ and _shining Wood_ will be easily quenched by _Water_ and _many other Liquors_.... 5. As a _quick Coal_ is not to be _extinguished_ by the Coldness of the _Air_, when it is greater than ordinary; so neither is a Piece of _shining Wood_ to be deprived of its _Light_ by the same Quality of the _Air_.... Differences: 1. The first Difference I observed betwixt a _live Coal_ and a _shining Wood_ is, that whereas the _Light_ of the _former_ is readily _extinguishable_ by _Compression_ (as is obvious in the Practice of suddenly _extinguishing_ a piece of _Coal_ by treading upon it), I could not find that such a _Compression_ as I could conveniently give without losing sight of its operation, would _put out_, or much injure the _Light_, even of small Fragments of _shining_ Wood.... 2. The next _Unlikeness_ to be taken notice of betwixt _rotten Wood_ and a _kindled Coal_ is, that the latter will, in a very few _Minutes_, be totally _extinguished_ by the withdrawing of the _Air_; whereas a Piece of _shining Wood_, being eclipsed by the Absence of the _Air_, and kept so for a Time, will immediately _recover_ its _Light_ if the _Air_ be let in upon it again within half an hour after it was first withdrawn....