the conductor and the machinery which
supports it. Another light for the purpose of
collecting the electricity by its flame, is placed
above the top of the pole. This light, burning
at night, has given rise to many a strange
supposition in the neighbourhood. It is too high
up to be serviceable as a lanthorn to those
below. Besides, who walks in Greenwich Park
after the gates are closed? It can light only
the birds or the deer. 'Then, surely,' says
another popular legend, ' it is to guide the
ships on the river, when on their way up at
night;—a sort of land-mark to tell
whereabouts the Observatory is when the moon
and stars are clouded, and refuse to show
where their watchers are.'

All these speculations are idle, for the lights
burn when the sun is shining, as well as at
night; and the object of the lower one is that
no trace of moisture, and no approach of cold,
shall give the electricity a chance of slipping
down the mast, or the ropes, to the earth, but
shall leave it no way of escape from the wise
men below, who want it, and will have it,
whether it likes or no, in their jars, that they
may measure its quantity and its quality, and
write both down in their journals. It is thus
that electricity comes down the wires into
those jars on our right as we enter. If very
slight, its presence there is indicated by tiny
morsels of pendent gold-leaf; if stronger, the
divergence of two straws show it; if stronger
still, the third jar holds its greater force, whilst
neighbouring instruments measure the length
of the electric sparks, or mark the amount of
the electric force. At the desk, close by, sits
the observer, who jots down the successive
indications. In his book he registers from
day to day, throughout the year, how much
electricity has been in the air, and what was
its character, even to such particulars as to
whether its sparks were blue, violet, or purple
in colour. At times, however, he has to
exercise great care, and it is not always that he
even then escapes receiving severe shocks.

Passing on, we approach the magnets. They
are three in number; of large size, and
differently suspended, to show the various ways
in which such bodies are acted upon. All
hang by bands of unwrought silk. If the silk
were twisted, it would twist the magnets,
and the accuracy of their position would be
disturbed. Magnets, like telescopes, must be
true in their adjustment to the hundredth
part of a hair's breadth. One magnet hangs
north and south; another east and west; and
a third, like a scale-beam, is balanced on
knife-edges and agate planes, so beautifully,
that when once adjusted and enclosed 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 amongst his
machines. Indeed, spiders occasionally betray
the magnetic observer into very odd behaviour.
At times he may be seen bowing in the
sunshine, like a Persian fire-worshipper; now
stooping in this direction, now dodging in that,
but always gazing through the sun's rays up
towards 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 neighbouring 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 whilst 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 Registrar-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 watchfulness. Now, in the
magnet-house, we see light and chemistry doing
the tasks before performed by human labour;
and doing them more faithfully than even the
most vigilant of human eyes and hands. Around
the magnets are cases of zinc, so perfect that
they exclude all light from without. Inside
those cases, in one place, is a lamp giving a
single ray of prepared light which, falling
upon a mirror soldered to the magnet, moves
with its motions. This wandering ray,
directed towards a sheet of sensitive
photographic paper, records the magnet's slightest
motion! The paper moves on by clockwork,
and once in four-and-twenty hours an
assistant, having closed the shutters of the
building, lights a lanthorn of yellow glass,
opens the magnet-boxes, removes the paper
on which the magnets have been enabled to
record their own motions, and then, having
put in a fresh sheet of sensitive paper, he shuts