rvations in single seconds;
the Dudley instrument will register to tenths of seconds. That
has six or eight microscopes; this has four. That has a gas lamp,
by the light of which the graduations are read off; the Albany
instrument has no lamp, and the Doctor considered the lamp a
hazardous experiment, affecting the integrity of the experiment,
not only by its radiant heat but by the currents of heated air
which it produces. The diameter of the object-glass of the Albany
instrument is 7-1/2 French inches clear aperture, or 8 English
inches, and the length of the tube 8 feet. He would have
preferred an instrument in which the facilities of manipulation
would have been greater, but was hampered by one proviso, upon
which the Trustees of the institution insisted--that this should
be the biggest instrument of its kind; and the instruction was
obeyed. The glass was made by Chance, and ground by Pistor
himself. The eye-piece is fitted with two micrometers, for
vertical and horizontal observations. Another apparatus provides
for the detection and measurement of the flexure of the tube.
Much trouble was experienced in securing a good casting for the
steel axis of the instrument. Three were found imperfect under
the lathe, and the fourth was chosen; but even then the pivots
were made in separate pieces, which were set in very deeply and
welded. Dr. Gould said he had been requested by the gentlemen who
had this enterprise in charge to suggest, as a mark of respect to
a gentleman of Albany who was a munificent patron of Science,
that this instrument be known as the Olcott Meridian Circle.

WHAT THE DUDLEY OBSERVATORY IS.

It stands a mile from the Capitol, in the city of Albany, upon the crest
of a hill, so difficult of approach, as to be in reality a Hill of
Science. There are two ways of getting to it. In both cases there are
rail fences to be clambered over, and long grass to wade through,
settlements to explore, and a clayey road to travel; but these are minor
troubles. The elevation of the hill above tide-water is, perhaps, 200
feet; its distance from the Capitol about a mile and a half. The view
for miles is unimpeded; and the Observatory is belted about with woods
and verdant lawns. There could not be a finer location or a purer air.
The plateau contains some fifteen acres.

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