determined by exposing slips of
glass, each having an area of a square centimeter, and coated with a
sticky mixture of glycerine, water, proof spirit, and a little carbolic
acid. Mr. Blackley gives two tables, showing the average number of pollen
grains collected in twenty-four hours on one square of glass, between May
28 and August 21, in both a rural and an urban position. The maximum both
in town and country was reached on June 28, when in the town 105 pollen
grains were deposited, and in the country 880 grains. The number of
grains deposited was found to vary much, falling almost to zero during
heavy rain and rising to a maximum if the rain were followed by bright
sunshine. Mr. Blackley found that the severity of his own symptoms
closely corresponded to the number of pollen grains deposited on his
glasses. Mr. Blackley devised some very ingenious experiments to
determine the number of grains floating in the air at different
altitudes. The experiments were conducted by means of a kite, to which
the slips of glass were attached, fixed in an ingenious apparatus, by
means of which the surface of the glass was kept covered until a
considerable altitude had been reached. Mr. Blackley's first experiment
gave as a result that 104 pollen grains were deposited in the glass
attached to the kite, while only 10 were deposited on a glass near the
ground. This experiment was repeated. Again and again, and always with
the same result, there was more pollen in the upper strata of the air
than in the lower.

A very interesting experiment was performed at Filey, in June, 1870. A
breeze was blowing from the sea, and had been blowing for 12 or 15
hours. Mr. Blackley flew his kite to an elevation of 1,000 feet. The
glass attached to the kite was exposed for three hours, and on it there
were 80 grains of pollen, whereas a similar glass, exposed at the margin
of the water, showed no pollen nor any organic form. Whence came this
pollen collected on the upper glass? Probably from Holland or Denmark.
Possibly from some point nearer the center of Europe.

POTATO DISEASE.

A study of the terrible disease which so often attacks the potato crop in
this country will serve, I think, to bring forcibly before you certain
untoward conditions which may be called climatic, and which are
attributable to fungoid spores in the air.

With the potato disease you are all, probably, more or less practically
acquainted. When summer is at its height, and w