106 
]Mr Troughton’s Nautical Toj). 
tion or inclination given to the box on which it was placed ; and 
therefore, that it might be of great advantage as an artificial ho- 
rizon. When it was spun in the open air, it continued in mo- 
tion 35 minutes ; but when it was made to revolve in vacuo^ its 
motion continued during the space of two hours and sixteen mi- 
nutes^ preserving a perfect horizontalitj for the space of three 
quarters of an hour. 
The nautical top, as made by more than one of the first ar- 
tists, was tried at sea about sixty years ago, by some of the first 
naval officers, with sanguine hopes of success. These hopes, 
however, were disappointed, and in a few years it shared the 
same fate as ail the other contrivances that preceded it. Mr 
Weir, who revived this subject, failed to a far greater extent 
than any who liad gone before him. His instrument, made by 
the order, and at the expence, of the Board of Longitude, was 
tried in a King's ship by himself and an astronomer appointed 
by the Admiralty. It was soon found, that when the ship had 
any motion, the top could not be depended upon to the amount of 
several degrees, although on shore it performed within a smaller 
number of minutes. Mr Weir's machine, which was very Hrge, 
had a reflecting surface of full 12 inches diameter; it required 
a man to keep it in motion while observations were made with 
it. The glass rested its weight upon a blunt point, supported 
from a chest below. The train of wheels that gave motion to 
the glass, were connected to the latter by means of leather 
thongs ; and the motion of the ship stretching one of the thongs, 
and relaxing the opposite one, drew the glass from its due posi- 
tion through the angle mentioned above. 
It was in the beginning of last year, that Mr Troughton be- 
gan his experiments on the Nautical Top, under an idea that this 
instrument had not hitherto had a decisive trjal ; and we think it 
will be allowed by all who are acquainted with the genius and re- 
sources of that eminent artist, that, if the idea is susceptible of 
being brought to perfection, it will be perfected in his hands.. His 
first efforts were very flattering ; for, by means of an easy adjust- 
ment, he brought the planes of reflection and rotation parallel to 
each other; a thing of so much importance, that it had been consi- 
dered as the chief cause of failure in the first constructions, and 
