est the difference between the
temperature of the Thames, and of the surrounding atmosphere, are
expected to show the cause of the famous London fog. During the night
the Thames is often from ten to seventeen degrees warmer, and in the day
time from eight to ten degrees colder than the air above it.

If the theory of weather-cycles holds good, we are to have seasons
colder than the average from this time till 1853, when warmth will begin
again to predominate over cold. A chilly prophecy this to close with,
and therefore, rather let an anecdote complete this chapter on the
Weather-Watchers of Greenwich.

Among other experiments going on some time ago in the observatory
inclosure, were some by which Mr. Glaisher sought to discover how much
warmth the earth lost during the hours of night, and how much moisture
the air would take up in a day from a given surface. Upon the long
grass, within the dwarf fence already mentioned were placed all sorts of
odd substances, in little distinct qualities. Ashes wood, leather,
linen, cotton, glass, lead, copper and stone, among other things, were
there to show how each affected the question of radiation. Close by upon
a post was a dish six inches across, in which every day there was
punctually poured one ounce of water, and at the same hour next day, as
punctually was this fluid remeasured to see what had been lost by
evaporation. For three years this latter experiment had been going on,
and the results were posted up in a book; but the figures gave most
contradictory results. There was either something very irregular in the
air, or something very wrong in the apparatus. It was watched for
leakage, but none was found, when one day Mr. Glaisher stepped out of
the magnet-house, and looking toward the stand, the mystery was
revealed. The evaporating dish of the philosopher was being used as a
bath by an irreverent bird! a sparrow was scattering from his wings the
water left to be drunk by the winds of Heaven. Only one thing remained
to be done; and the next minute saw a pen run through the tables that
had taken three years to compile. The labor was lost--the work had to be
begun again.

DOING.

Oh, friend, whoe'er thou art, who dost rejoice
In the sweet tones of thy melodious voice;
Which to thy fancy are so rich and clear,
Falling like music, on the list'ning ear,
Of thee I ask,
What hast thou done of that thou hast to do?