F 11
Stars were observed on each night between September 4 and October 27, inclusive. This is apparently a record for Hongkong and reflects great credit on the observers. The period included several cloudy nights on which opportunities for observing might easily have been missed.
Transits of the sun were only observed when star transits were not available from the previous night.
The azimuth and collimation determinations were made by the Director and the Chief Assistant. The azimuth determinations depend usually on observations of the old south mark.
Clocks. The performance of the Standard Sidereal clock Dent No. 39741 has again been exceptionally good.
Its rate varied from +08 .04 on January 11 (Bar. 308 .41, Temp. 54°.1) to -08 .58 on August 5 (Bar. 29ins. .59, Temp. 83°.6). The rate during cloudy periods was partly derived from the formula:
r = r0 + 0·4 (p0−p) −0·00392 (t0-t).
where r is the losing rate at pressure p, in inches, and temperature t, in degrees Fahrenheit, and r0, the losing rate at pressure p0 and temperature t0.
It was found however that the rate could not be accurately computed from this formula after rapid changes of temperature and pressure, and until the clock is properly mounted in an underground room there will always be considerable uncertainty at times as to its rate.
In the following table is given the excess of the observed over the inferred rate after cloudy periods in the year 1917:
Date 1917. Interval withoutF 11
Stars were observed on each night between September 4 and October 27, inclusive. This is apparently a record for Hongkong and reflects great credit on the observers. The period included several cloudy nights on which opportunities for observing might easily have been missed.
Transits of the sun were only observed when star transits were not available from the previous night.
The azimuth and collimation determinations were made by the Director and the Chief Assistant. The azimuth determinations depend usually on observations of the old south mark.
Clocks. The performance of the Standard Sidereal clock Dent No. 39741 has again been exceptionally good.
Its rate varied from +0 04 on January 11 (Bar. 30s 41, Temp. 54°1) to -0° 58 on August 5 (Bar. 29ins. 59, Temp. 83°-6). The rate during cloudy periods was partly derived from the formula:
•
:-
r=r。 + 0·4 (pc−p) −0·00392 (t。-t).
where is the losing rate at pressure p, in inches, and tem- perature t, in degrees Fahrenheit, and r, the losing rate at pressure Po and temperature t。.
It was found however that the rate could not be accurately computed from this formula after rapid changes of temperature and pressure, and until the clock is properly mounted in an underground room there will always be considerable uncertainty at times as to its rate.
In the following table is given the excess of the observed over the inferred rate after cloudy periods in the year 1917:-
Date 1917.
Interval without
Excess of observed over
observations.
inferred error.
January 8
6 days
-0.91
March
+0.06
3
4
"}
13
3
-0'19
*7
27
+
+0.04
April
19
7
- O'10
}}
26
5
+0·63
May
19
4
??
>>
27
3
;
June
24
༢
A A
July
24
3
-O'14 +0°42
+0'10
+0.27
29
""
November December
+0.94
+0.16
"1
I
3
-0.06
29
17
6
14
·0'12
:་
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