and round and round, plenty of sand and water being supplied between
the mirror and the tool to produce the necessary attrition. As the
process proceeded and as the surface became smooth, emery was used
instead of sand; and when this stage was complete, the grinding tool
was removed and the polishing tool was substituted. The essential
part of this was a surface of pitch, which, having been temporarily
softened by heat, was then placed on the mirror, and accepted from
the mirror the proper form. Rouge was then introduced as the
polishing powder, and the operation was continued about nine hours,
by which time the great mirror had acquired the appearance of highly
polished silver. When completed, the disc of speculum metal was
about six feet across and four inches thick. The depression in the
centre was about half an inch. Mounted on a little truck, the great
speculum was then conveyed to the instrument, to be placed in its
receptacle at the bottom of the tube, the length of which was sixty
feet, this being the focal distance of the mirror. Another small
reflector was inserted in the great tube sideways, so as to direct
the gaze of the observer down upon the great reflector. Thus was
completed the most colossal instrument for the exploration of the
heavens which the art of man has ever constructed.

[PLATE: ROMAN CATHOLIC CHURCH AT PARSONSTOWN.]

It was once my privilege to be one of those to whom the illustrious
builder of the great telescope entrusted its use. For two seasons in
1865 and 1866 I had the honour of being Lord Rosse's astronomer.
During that time I passed many a fine night in the observer's
gallery, examining different objects in the heavens with the aid of
this remarkable instrument. At the time I was there, the objects
principally studied were the nebulae, those faint stains of light