pose 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 neighborhood. It is too high up to be serviceable as a lantern 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 landmark to tell where-abouts 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, while neighboring 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 color. 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 kn