representing the most advanced views of his age, are
of interest.

"The theory of the air seemeth at present," he says,
"to be perfectly well understood, and the differing
densities thereof at all altitudes; for supposing the
same air to occupy spaces reciprocally proportional to
the quantity of the superior or incumbent air, I have
elsewhere proved that at forty miles high the air is
rarer than at the surface of the earth at three thousand
times; and that the utmost height of the atmosphere,
which reflects light in the Crepusculum, is not fully
forty-five miles, notwithstanding which 'tis still
manifest that some sort of vapors, and those in no
small quantity, arise nearly to that height. An instance
of this may be given in the great light the
society had an account of (vide Transact. Sep., 1676)
from Dr. Wallis, which was seen in very distant counties
almost over all the south part of England. Of
which though the doctor could not get so particular a
relation as was requisite to determine the height thereof,
yet from the distant places it was seen in, it could
not but be very many miles high.

"So likewise that meteor which was seen in 1708, on
the 31st of July, between nine and ten o'clock at night,
was evidently between forty and fifty miles perpendicularly
high, and as near as I can gather, over Shereness
and the buoy on the Nore. For it was seen at London
moving horizontally from east by north to east by