younger Herschel, and had gone with the latter in
September, 1834, to the Cape of Good Hope, whither he had been sent by
the British Government, acting in conjunction with the Governments of
France and Austria, to observe the transit of Mercury over the disc of
the sun--an astronomical point of great importance to the lunar
observations of longitude, and consequently to the navigation of the
world. This transit was not calculated to occur before the 7th of
November, 1835 (the year in which the hoax was printed;) but Sir John
Herschel set out nearly a year in advance, for the purpose of thoroughly
testing a new and stupendous telescope devised by himself under this
peculiar inspiration, and infinitely surpassing anything of the kind
ever before attempted by mortal man. It has been discovered by previous
astronomers and among others, by Herschel's illustrious father, that the
sidereal object becomes dim in proportion as it is magnified, and that,
beyond a certain limit, the magnifying power is consequently rendered
almost useless. Thus, an impassable barrier seemed to lie in the way of
future close observation, unless some means could be devised to
illuminate the object to the eye. By intense research and the
application of all recent improvements in optics, Sir John had succeeded
in securing a beautiful and perfectly lighted image of the moon with a
magnifying power that increased its apparent size in the heavens six
thousand times. Dividing the distance of the moon from the earth, viz.:
240,000 miles, by six thousand, we we have forty miles as the distance
at which she would then seem to be seen; and as the elder Herschel, with
a magnifying power, only one thousand, had calculated that he could
distinguish an object on the moon's surface not more than 122 yards in
diameter, it was clear that his son, with six times the power, could see
an object there only twenty-two yards in diameter. But, for any further
advance in power and light, the way seemed insuperably closed until a
profound conversation with the great savant and optician, Sir David
Brewster, led Herschel to suggest to the latter the idea of the
readoption of the old fashioned telescopes, without tubes, which threw
their images upon reflectors in a dark apartment, and then the
illumination of these images by the intense hydro-oxygen light used in
the ordinary illuminated microscope. At this suggestion, Brewster is
represented by the veracious chronicler as leapin