such a limit exists; much more he conceived it to be certain that
our atmosphere does not contain the vapour of the fixed constituents
of the earth's crust. This question, I may say, is likely to remain
an open one. Dr. Rankine, for example, has lately drawn attention
to the odour of certain metals; whence comes this odour, if it be
not from the vapour of the metal?

In 1825 Faraday became a member of a committee, to which Sir John
Herschel and Mr. Dollond also belonged, appointed by the Royal Society
to examine, and if possible improve, the manufacture of glass for
optical purposes. Their experiments continued till 1829, when the
account of them constituted the subject of a 'Bakerian Lecture.'
This lectureship, founded in 1774 by Henry Baker, Esq., of the
Strand, London, provides that every year a lecture shall be given
before the Royal Society, the sum of four pounds being paid to the
lecturer. The Bakerian Lecture, however, has long since passed from
the region of pay to that of honour, papers of mark only being
chosen for it by the council of the Society. Faraday's first
Bakerian Lecture, 'On the Manufacture of Glass for Optical Purposes,'
was delivered at the close of 1829. It is a most elaborate and
conscientious description of processes, precautions, and results:
the details were so exact and so minute, and the paper consequently
so long, that three successive sittings of the Royal Society were
taken up by the delivery of the lecture.[3] This glass did not turn
out to be of important practical use, but it happened afterwards to
be the foundation of two of Faraday's greatest discoveries.[4]

The experiments here referred to were commenced at the Falcon Glass
Works, on the premises of Messrs. Green and Pellatt, but Faraday
could not conveniently attend to them there. In 1827, therefore,