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TABLE V.

Seasonal Variation of the Coefficients of the Diurnal Variation of the Barometer as functions

of the Sun's mean Longitude. (Unit = 0.0001 inch).

Coefficient.

Constant Term.

COS O

sin e

cos 2 0

sin 2 0

cos 30

sin 30

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(c) DURBAN, NATAL OBSERVATORY, 1873-1905.

48 55

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The monthly means given in the table are derived from two sets of observations. From 1873-1883 the readings were taken in the Botanical Gardens, Durban, which are close to the Observatory, (Govt. Astronomer's Report for 1903). Observations were made at 9 a.m. and 3 p.m. It has been assumed from the observations themselves, that in the mean the difference of the reading 9 a.m.-3 p.m. is as follows :Jan. - 0.043in.

July -0.055in.
Feb.
45

Aug. 60
Mar.

Sept. 57
Apl.

Oct.

55
May
54

Nov.

53
June
50

Dec. 46 The mean of the 3 p.m. readings thus increased, and the 9 a.m. readings has been taken as the 9 a.m. reading. When this mean deviates more than 0.015in. from the 9 a.m. reading is added as added to the figures printed in Table 1. It has been further assumed that in the mean of 11 years, these readings reduced to sea-level should agree with the mean of all the reduced readings taken at the Durban Observatory. To force this agreement -0.038in. has been applied to all the readings taken at the Botanical Gardens. The observations since 1884 have been made at the Natal Observatory In deriving the 9 a.m. means, we have in general three sets of figures, viz., the 8 a.m. readings published by the Cape Meteorological Commission, and the 9 a.m. and 3 p.m. readings published by the Government Astronomer. It has been assumed that in the mean the difference between the 9 a.m. reading and the 8 a.m. and 3 p.m. readings are as follows:

3 p.m.

8 a.m.

3 p.m. Jany. +0.038in. +0.05oin. July +0.ozrin. +0.075in. Feby. 38 55 Aug.

32

77 Mar.

60 Sept.

34

78 Apl.

64
Oct.
35

73 May 33 68 Nov. 36

66 July 32

72
Dec.
37

55 The mean 9 a.m. reading is the mean of the three reduced readings, but discordant readings have been rejected. The heights of the Durban barometers have been

261 feet to Nov., 1884.
250

to 31st Dec., 1896.

262 from ist Jan., 1897. The reduction from mean of year at 9 a.m. to mean of day is about -0.033 inches.

I have to thank Mr. Nevill and Mr. Fermor Rendell for their assistance in clearing up some doubtful printings and readings.

8 a.m.

37

36

TABLE 1.--Mean Monthly Readings of the Durban Barometer at 9 a.m., reduced to 32° F.,

sea-level and gravity of 45° Lat.

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29.973

30'028

061

*048: 30.114

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252

240

154

*087

30.063

30.020

106

3

30.018

29.998

064

*079

30.107

240

210

191

'118

127

30.066

30.003

101

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1881

29.972

30.017

30 026

30 130

30.002

30.255

30 195

30.188

30 183

30.078

29.983

29.978

30.084

1890

29 961

29.935

Mean.

29'994

29.998

30-061

30-090

30.112

30-244

30-240

30 197

30:181

30.109

30-034

30.005

30.105

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167

30-066

29.997

30.113

2

29.928

29.959

30.005

066

118

138

259

'151

*089

078

29.973

29.948

*059

3

29.925

29.979

30.090

*075

197

176

272

'186

090

*090

30-017

29.990

091

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1891

29.991

29.958

30:073

30.121

30100

30.152

30.334

30 254

30.143

1900

29.953

30.057

30.033

Mean.

29.965

30.009

30.034

30 112

30 166

30 226

30 232

30-206

30 140

*076

*017

29.985

30.097

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