280 PROCEEDINGS OF SECTION E. 
2 ft. 4.5 in. along the southern wall of the room, and as it was 
thus placed just in front of the door, a trap-door had to be 
constructed admitting of an easy entrance. The sides of this 
excavation are lined with timber, and a floor is. laid, and covered 
with oilcloth and carpet so as to keep out the wet as much as 
possible. The only window is at the west end of the room, in 
addition to which there are two small holes towards north, 
which materially assist in airing the place. Just in front of 
the door is a pier, for the purpose of receiving 
Tue TELESCOPE FOR OBSERVING THE COINCIDENCES. 
This is a small, but very superior glass by Merz Sons, Munich, 
of a magnifying power of eighteen times, and is fixed to a 
small stand in such a way as to admit of a horizontal and 
vertical motion, and also a sliding motion at right angles to the 
axis of the whole apparatus. This axis, as indicated by the 
direction of the telescope, which is parallel to the southern wall, 
bears about from W. 12 deg. 8. to E. 12 deg. N. On this line, 
and at the end of the excavation towards east, is mounted 
THE CLOCK; 
facing the observer of the telescope. Particular attention was 
paid to obtain a firm foundation for the clock, and for this 
purpose a layer of bricks was put on the ground, on which 
was placed a heavy timber frame, the intermediate space being 
filled up with “ plaster of Paris,” the object of which is obvious. 
On this rested a stone 3 ft. by 1 ft. 7 in, and 6 in. high, in 
such a way that a piece of wood 2 ft. 6 in. long, and 2 ft. 5.5 in. 
broad, and 4 in. thick, could be fixed in a vertical position to 
the frame above mentioned. To this was attached the back 
of the clock ; both the back of the clock and the piece of timber 
were perforated in a level with the telescope, and about 3 in. 
below the clock pendulum, so as to admit of a free sight towards 
the reversion pendulum, which is presently to be described. 
The clock is of the workmanship of W. Sheperd, of London, 
and was lent to me for these observations by the late W. 
M‘Gowan, Superintendent of Electric Telegraphs, and to the 
courtesy of this gentleman, as well as of Mr. Ellery, the 
Government Astronomer, I am greatly indebted for connecting 
the clock with the transit-room of the Observatory by electric 
wires, which arrangement greatly facilitates the determination 
of the rate of the clock. 
On the lower extremity of the clock pendulum is fixed to a 
brass point a square piece of cardboard, in which is cut a hole 
0.3 in. high, and about 0.06 in. broad; this incision is made 
perpendicular, and in such a manner that whenever the clock 
pendulum passes the middle line, or is at rest, an observer 
