ife-edges and agate planes, so beautifully,
that when once adjusted and inclosed in its case, it is opened only once
a year, lest one grain of dust, or one small spider, should destroy its
truth; for spiders are as troublesome to the weather-student as to the
astronomer. These insects like the perfect quiet that reigns about the
instruments of the philosopher, and with heroic perseverance persist in
spinning their fine threads among his machines. Indeed, spiders
occasionally betray the magnetic observer into very odd behavior At
times he may be seen bowing in the sunshine, like a Persian
fire-worshiper; now stooping in this direction, now dodging in that, but
always gazing through the sun's rays up toward that luminary. He seems
demented, staring at nothing. At last he lifts his hand; he snatches
apparently at vacancy to pull nothing down In truth his eye had at last
caught the gleam of light reflected from an almost invisible spider line
running from the electrical wire to the neighboring planks. The spider
who had ventured on the charged wire paid the penalty of such daring
with his life long ago, but he had left his web behind him, and that
beautifully minute thread has been carrying off to the earth a portion
of the electric fluid, before it had been received, and tested, and
registered by the mechanism below. Such facts show the exceeding
delicacy of the observations.

For seven years, the magnets suspended in this building were constantly
watched every two hours--every even hour--day and night, except on
Sundays, the object being that some light might be thrown upon the laws
regulating the movements of the mariner's compass; hence, that while men
became wiser, navigation might be rendered safer. The chief
observer--the _genius loci_--is Mr. Glaisher, whose name figures in the
reports of the Register-General. He, with two assistants, from year to
year, went on making these tedious examinations of the variations of the
magnets, by means of small telescopes, fixed with great precision upon
pedestals of masonry or wood fixed on the earth, and unconnected with
the floor of the building, occupying a position exactly between the
three magnets. This mode of proceeding had continued for some years with
almost unerring regularity, and certain large quarto volumes full of
figures were the results, when an ingenious medical man, Mr. Brooke, hit
upon a photographic plan for removing the necessity for this perpetual
watchfulnes