AT THE OBSERVATORY AT PARAMATTA. 
35 
Methods of Observing the Repetitions. 
During the last years when I was without an assistant, the intervals, and 
therewith the second parts of the reductions p 2 cot z (s — c$) would have become 
too great in the southern solstice, if I had attended at the same time to the 
level, which moreover became useless under the sun’s vertical rays. This is 
therefore an additional reason why I have resorted to reflection from mercury. 
The small nadir distance enabling me to place it upon the same isolated pillar 
with the instrument, and to keep all the openings of the dome shut except the 
top slide, the mercury was secured against wind, and all percussion save that 
occasioned by handling the instrument, and no glass cover was required. During 
the same series I did not revolve 180° in azimuth, .but pointed the tube in a left- 
sided series, first by means of the great circle to the reflected image, and next 
by shifting the small circle to the direct object, and I then again turned the 
great circle for the observation by reflection, repeating this process until a 
series was completed, containing a multiple of altitudes instead of zenith di- 
stances. In a right-sided series it is the great circle by which the tube must be 
first pointed to the direct object. The repetitions can thus be carried on with 
remarkable expedition by one observer. All that is required is that the in- 
strument remains steady during the interval between a reflected and direct 
vision. The reflection and direct vision enabled me by three observations to 
verify that the optical axis described a vertical circle, and the effects of bending 
compensated themselves. I shall illustrate the process by an 
Example. 
December 22, 1827 : Barom. 29.726. Therm. 83°. Transit per Clock 17 h 58 m l s .9. 
Readings. 
0 , ,, Times per sidereal Clock. 
■0. 32 15 25 
h 
m 
s 
m 
s 
m 
s 
m 
s 
I. 
346 
59 
2 . 
-17 
35 
52.5 
36 
36 
37 
34 
38 
10 
m 
s 
m 
s 
m 
S 
ra 
S 
m 
S 
m 
S 
IT. 
59 
26 
8.5. 
41 
4 
41 
48.3 
42 
52.7 
43 
28.3 
44 
24.5 
45 
9 
46 
8.8 
46 
44 
47 
43 
48 
51.0 
III. 
134 
44 
26.5. 
52 
13 
53 
2.0 
53 
47.0 
54 
34.0 
4 
1.0 
4 
40 
5 
59.0 
6 
54 
7 
58 
8 
53.3 
W IV. 
204 
31 
31 . 
.18 
12 
2 
12 
42.0 
13 
43.0 
14 
13.0 
14 
57.4 
15 
34 
16 
29.0 
17 
45 
17 
47 
18 
28.0 
