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.
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