were in fact present in a great natural aero-physical laboratory where daily experiments were being performed on a large scale. In building this meteorological laboratory at San Francisco nature also provided seats wherefrom we can obtain excellent views of the experiments while in progress. From the Weather Bureau station on Mount Tamalpais-elevation of station, 2,373 feet-one looks down on the broad expanse of the Pacific, nearly 20,000,000 square miles of water, to the north, west, and south. From the open roadstead of Drakes Bay the eye passes over the Sausalito hills to the headlands of Points Bonita and Lobos, marking the entrance to the Golden Gate. This passage plays an important rôle in connection with the winds, temperatures, and fogs of the San Francisco Bay region. At mean tide the area of San Francisco Bay is about 450 square miles.

Far on the eastern horizon, especially on clear winter days, the snow of the Sierra-155 miles distant-can be seen glistening. These mountains vary in height from 8,000 to 14,000 feet.

Extending from the slopes of the Sierra to the Coast Range is a great basin 500 miles long and about 50 wide. The Sacramento and San Joaquin rivers, flowing through this basin, unite in Suisun Bay. This great inland basin, surrounded by mountain walls, is connected with the Pacific Ocean by the gate at San Francisco, San Francisco Bay, San Pablo Bay, Carquinez Straits, and Suisun Bay. Here, then, is an aero-physical laboratory par excellence. Now for the results.

When a native of San Francisco is asked which is the coldest month of the year, he is generally at a loss for an answer; and if asked which is the warmest he may say November. This confusion arises from the comparatively small range of temperature. The mean annual temperature, as determined from the records of the Weather Bureau for thirty-one years is 56.1 F. May and November have practically the same temperature. The warmest month is September, 60.8; the coldest, January, 50.2°. The other months have mean temperatures as follows: February, 52; March, 54; April, 55; May, 57°; June, July, and August, 59°; October, 60°; November, 56°; December, 52°.

The highest temperature ever recorded at San Francisco was 100°, on June 29, 1891, and the lowest 29°, on January 15, 1888. Abnormally warm and cold periods last, as a rule, about three days. The mean of the three consecutive warmest days at San Francisco has never exceeded 76.3. A period of warm weather during the summer months is, as a rule, brought to a close about the evening of the third day with strong west winds, dense fog, and temperatures ranging from 49° to 54. The mean of the three consecutive coldest days was 40.7. The greatest daily range of temperature was 43, on June 29, 1891. This was the date when the temperature reached 100. The range of temperature was from 100 to 57. The morning was calm and very warm, while at 5 p. m. the temperature was 80° and next morning 74°.

In the past thirty years the number of days on which snow has fallen can be counted on the ten fingers. Thunderstorms likewise are infrequent, but not altogether unknown. Earthquakes, meaning by this all slight shocks and tremors, average about 7 per annum. Very little damage has been done by earthquakes during the past fifty years.

The people in San Francisco have long realized that winter and summer are purely relative terms. Thus at any of the ferries on a midsummer day one can see summer fabrics worn with heavy wraps, and it is not unusual to see white duck and sealskin in combination. Visitors to the city should by all means wear heavy wraps or overcoats during the summer afternoon.

The experiments of the observers of the Weather Bureau during the past two years with kites have thrown much light upon the causes of the climatic abnormalities experienced at San Francisco; and, among other things, it has become evident that in summer as we ascend from the ground the temperature rises. For each 155 feet of elevation the temperature is 1° F. warmer, and so on any of the hills or mountains in the vicinity of San Francisco one can find with very little effort the climate best suited for him. In other words, the citizen of the San Francisco Bay section can regulate the temperature to suit himself, having a choice between these limits: 55° at sea level and 85° at 2,000 feet above.

With regard to rainfall, during the summer months, San Francisco is practically rainless. By referring to the accompanying charts it will be seen that in June, July, August, and September showers are very rare. The average rainfall is about 23 inches, and most of this falls during the months of November, December, January, February, and March. Looking over the records of the past fifty years we find that the year 1898 had but 9.31 inches, while in 1883 there was 38.82 inches. In 1861 there was 38.51 inches.

1871.

1872.

1873.

1874.

1875.

1876.

2877.

1878.

The annual rainfalls do not, however, fairly represent the amount of rainfall determining crop yield. Both with fruits and grains it is the seasonal rainfall rather than the annual which is to be considered. In the wheat fields summer fallowing is resorted to chiefly for the reason that the rain of two seasons can be utilized. As may be seen by the tables of annual and seasonal rainfall, published in following pages, the amounts during the growing season vary from the totals for the calendar year; thus, in 1889-90 the seasonal rainfall was 45.85 inches. The annual rainfall for 1890 was but 25.43 inches, an unusually heavy rainfall in December, 1889, having contributed to materially increase the seasonal amount.

Frequency as well as intensity should also be taken into account in considering the relation of rainfall and crops.

1879.

1880.

1881.

1882.

1883.

1884.

1885.

1886.

1887.

1888.

1889.

1890.

1891

1892.

1893.

1894.

1895.

1896.

1897.

1898.

1899.

1900.

1901..

Means, 31 years, except Jan

uary and February.

MONTHLY MEAN TEMPERATURES (DEGREES FAHRENHEIT).

Jan. Feb. Mar.

May. June. July. Aug. Sept.

51.3

52.2

54.2

54.3

54,8

50.9

54.5

49.3 51.2

49.0

52.0

51.4

48.8 52.8

53.0

54.3

52.7

55.8
53.3

52.8

57.2

48.8 54.6
48.8 49.4
54.0 55.3 54.4

51.6
50.0
53.2

48.0

51.0
52.8

49.4

48.8

47.0

48.8

50.6

50.8

53.3 54.3 56.9 56.6 57.9
60.4. 61.8 55.1 52.9
53.4 56.0 59.8 57.9 59.8 59.3 58.8 56.0 52.1
54.6 55.4 57.1 58.1
59.5
58.3 59.7 57.7 50.7
50.9 54,9 57.6 59.1 57.8 59.0 61.4 59.8 56.1 50.3
51.8 55.4 57.2 59.4 58.8 58.8 59.2 62.0 57.4
53.2 55.4 56.8
61.4 59.1 59.6 61.5 59.9 58.0
57.2
54.4 56.2 62.0 60.8 59.8 62.5 59.2 57.2
55.9
56.0 58.0 58.8 58.6 59.1 60.2
61.6 57.1
56.5
56.4
60.2 58.7 60.5 61.0 61.0 55.0
53.3 57.7 57.2 58.8 59.1 58.9 59.8 54.2
57.9
58.0 !- 58.6 59.7 58.8 59.7 56.6 55.1
53.4 53.0 57.0 57.9 59.5 58.6 59.8 58.8 53.2
54.0 53.2 58.0 61.4 59.8 59.2 63.1. 57.9 54.1
54.5 56.0 59.4 60.2 61.4 60.0 59.6 58.2 57.4
57.7
58.2 58.1 57.8 61.6 59.6 61.8 60.7 57.8
53.6 55.4 59.1 59.4 60.3 60.6 62.4 58.6 56.8
55.8 55.8 57.0 59.4 56.6 57.8 62.0 64.2 56.4
53.9 53.4 57.8 56.9
62.4
61.4 60.8 62.6 61.6 57.0
54.0
57.2 58.8. 58.8 60.2 58.8 60.4 61.6 61.8 58.6
46.2 49.1 53.8 54.8 59.8 59.2
59.8 61.4 60.4 62.4 59.0
52.2 51.1 55.0
53.4
55.7 60.2 59.4
61.8 61.8 59.7 58.6
51.7 52.4. 54.2 53.1
58.0 56.8 58.1 59.4 60.2 59.6 56.9
50.3 51.2 52.4 55.8 56.5 56.6 56.6 59.3 57.6 55.6
48.4
55.2 55.4 55.9 56.4 59.2 63.4 59.6
52.2
54.8 57.6 58.7 58.4 58.4 60.7 58.8
54.3 51.6 56.3
48.9 57.4 57.4
51.2 54.4 52.6

51.1

55.3

50.8 52.8 54.0 53.6 52.2 53.2

51.2

56.8

52.6

47.8

46.7

50.4

51.3

49.8
49.6
51.1.

47.4:

52.4 1

47.7

50.6

49.7

48.6 53.8

48.6

52.2

55.3

52.8

50.7

48.6
46.7

59.4
56.2
57.2 59.4
59.5
59.6 58.8 53.4
58.9 58.2 57.4 60.8 58.4 53.1
59.0 56.2 57.0 59.0 61.2
55.4
56.9 55.9 58.3 58.2 59.3 56.8
50.7 53.6 55.2 54.0 57.0 57.6 58.2
59.7 63.3 58.8 56.3
49.8 52.2 55.8 51.8 53.9 56.7 55.6 1 56.4 58.5 61.8 57.2

50.7
52.6

49.7

53.0 51.6 52.2 54.6 52.6

49.6
50.2

52.9

SEASONAL RAINFALL.

Apr.

Oct. Nov. Dec. Annual.

!

56.0 56.2

55.9

55.6

56.0

56.6

57.7

56.9

56.7

54.9

56.6

55.2

55.6

56.7

57.8

57.3

56.5

57.3

57.9

56.3

56.6

56.0

54.3

55.1

55.6

55.9

55.0

54.6

55.0

56.2

55.2

56.1

1h a. m.

Tempera-
ture.

a Record subsequent to January 1, 1891.

11

10

11

12

13

14

11

Clear Partly
cloudy
days.

days.

46.2
47.8

26, 1899
18,1899

48.9

7, 1892

51.6

14, 1888

52.6
55.9

28, 1887
29, 1891

56.2 15, 1888
56.6

22, 1891

58.3

22, 1894

56.6

8, 1899

53.1

48.6

16, 1895
8, 1893
b 1891

54.3

Average number of

2h

10

10

11

12

12

11

Date.

14

mum.

3h

Tempera-
ture.

4h

WEATHER.

78.0
80.0

80.0

88.0

97.0

100.0

93.0

92.0

94.0

94.0
83.0
72.0

100.0

!

7

11 August.

10

421

Absolute mini

10 October..

Date.

15, 1888
5,1887
3, 1896
7, 1891
1, 1899

19, 1893

31, 1893

8, 1893

30, 1894

14, 1881

27, 1896
24, 1879
c1888

5h

b June 29.

September..

mum.

November.

December

Greatest daily Tempera- range. ture.

Annual.

ᏮᏂ

Month.

24.0

9.9

27.0

10.7

11.3

29.0
33.0
33.0 28.0
40.0 34.0 11.7
43.0 39.0 12.0
43.0 12.5

47.0

47.0

47.0

49.0

36.0 11.5
38.0 11.4
35.0 13.3
31.0 13.3
25.0 11.3
21.0

45.0
38.0

34.0

9.3

29.0

43.0

11.5

7h

Mean Mean daily variarange. bility.

AVERAGE TEMPERATURE (DEGREES FAHRENHEIT) FOR EACH HOUR OF SEVENTY-FIFTH MERIDIAN TIME.

[λ=37° 48′ N.; p=122° 26′ W.]

2.2

2.0

2.5

2.7

2.9

2.4

2.4

2.4

3.0
3.5

2.6

2.2

2.6

149

Mean of Mean of three three consecu- consecutive tive warmest coldest days.a

days.a

Average number of

10h

122

67.0

64.7

67.7

68.7

73.7

76.0

66.3

76.0

76.3

71.7

69.3

62.0

76.3

Partly
cloudy cloudy Rainy
days.

idays.

days.

15

11

9

10

137

11h

6

4

6

9

79

42.0

40.7

40.7

48.3

49.7

52.3

50.0

52.7

54.0

51.7

44.7

42.3

40.7

50.1 49.8 49.2 49.0 48.5 48.2 48.2 48.8 48.2 47.6 47.5 48.0
52.0 51.3 50.9 50.7 50.0 49.6 49.5
49.9 49.0 48.6
48.7 49.9
52.8 51.8 51.4 50.7 50.6 50.4 50.1 51.2 50.2 49.7 50.5 52.0
51.4
51.1
50.6 50.3 50.1
49.7 49.4 50.1 49.1 49.8 51.5 53.4
53.9 53.3 52.7 52.3 51.8 51.5 51.5 52.2 51.2 53.2 55.4 57.4
54.4 53.6 53.1 52.7! 52.4 52.1 52.0 53.1 52.5 54.0 55.8 56.8
53.8 53.6 53.5
53.11 52.8 52.6 52.6
53.5 52.4 54.7 57.1 59.0
56.8 56.4 56.0 55.7 55.1 54.9 55.1 55.8 54.7 55.6 57.5 59.4
60.0 59.3 58.8 58.5 58.1 57.9 57.6 58.7
57.4 58.5 60.5 62.5
56.1 55.8 55.1 54.6
I
53.9 53.7 53.5 54.7 53.5 53.9 55.2 56.5
54.9 54.2 54.0 53.3 52.9 52.4 53.9 52.5 52.0 52.6 54.1
48.8 48.2 47.5 47.1 46.9 47.1 48.4 47.2 46.9 47.1 48.3
52.4 52.0 51.7 51.6 52.5 51.5 52.0 53.3 54.8

55.5

49.5

53.9

53.3 52.8

0

2

4

7

11

69

Noon. 1h p. m.

49.1 51.4 53.7 55.4 59.4 58.9 60.8 61.3 64.8

58.7

55.4 49.4 56.5

January
February

March

April

May

June.

July

August

AVERAGE TEMPERATURE (DEGREES FAHRENHEIT) FOR EACH HOUR OF SEVENTY-FIFTH MERIDIAN TIME-Continued.

[h=161 ft.; local time, 3h 10m slow.]

September..

October....

November
December

Year..

January
February.

March.

April

May

June

July.

August

September..

October

November..
December

Year..

January
February

March.

April

May.

June

July

August.
September...
October
November..
December

1900.

Year.

2h

56.3

50.5

3h

1ha.m

2h

4h

2h

བུ

AVERAGE PRESSURE (INCHES AND THOUSANDTHS) FOR EACH HOUR OF SEVENTY-FIFTH MERIDIAN TIME.
[A-37° 48′ N.; p. 122° 26′ W.; local time, 3h 10m slow.
1

H==155 ft.]

5h

3h

53.6
57.8
57.8
56.9

50.3 51.6
52.8
53.2 55.0 56.9
55.5 57.4 58.9
56.6 57.5 58.1
60.8 61.8 62.1
60.5
62.1
62.2
62.3 62.8
63.6 63.7

56.1 54.9 54.5

53.4 53.9
58.2 58.6
59.9 59.5
57.8 57.5
61.9 61.8 60.0
62.0 61.5 60.2
62.4 61.4 60.7
62.5 61.4
66.9 65.3
63.4 63.8
61.7
58.0 59.2 60.1 60.1 59.6
52.0
52.9 53.6 54.0 53.3 52.8 52.5 51.6 50.8 50.0 49.8 55.1 45.4
57.9 59.3
59.0 58.2 57.1 56.0 55.1 54.5 55.2 62.1 50.4
¡

52.9 52.5 51.9 51.3 50.5 50.3 54.7 46.7
56.9 55.3 54.5 53.7 53.1 52.7 59.5 47.8
57.0 55.5
54.5 53.8 53.2 53.7 61.3 49.1
55.8 55.0 53.8 52.6 52.2 53.2 59.5 48.4
59.0 57.8
56.1 63.5 50.6
59.6 58.3 57.0 55.8 55.1 56.5 i 63.7 51.6
59.8 58.2 56.5 55.4
54.6 56.9 64.6 51.9
60.7 59.5 58.6 57.5 57.2 58.5 65.5 53.9
64.7 63.1 62.0 61.3 60.5 62.0 70.4 56.2
60.4 59.3 58.4 57.5 56.9 57.6 65.1
52.4

61.9

62.8

63.2

66.4

68.3

68.3

67.9

60.3

62.4

63.1

58.7 57.9 57.2 56.6: 56.0 55.7 62.2 50.4

60.1

60.4

60.1

6h

4h

5h

5h

8h

[Correction applied to reduce to standard gravity-0.02.]

gh

7h

Th

Sh

10h

gh

gh

0.006
0.029

0.900

0.866

29.985 0.987 0.983 0.978
29.998 0.001 0.001 0.999
29.881 0.881 0.880 0.879
29.849 0.850 0.848 0.843
29.863 0.861 0.860 0.855
29.815 0.814 0.806 0.804
29.737 0.739 0.737, 0.735
29.805 0.804 0.803. 0.800
29.796 0.797 0.799 0.799
29.859 0.862 0.861 0.862

0.980 0.982 0.975 0.969 0.971 0.978 0.990
0.000 0.995 0.991 0.992 0.998 0.006 0.020
0.875 0.866 0.863 0.864 0.871 0.878 0.890
0.837 0.832 0.831 0.832 0.843 0.853 0.860
0.849 0.846 0.845 0.846 0.855 0.865 0.872 0.875
0.800 0.795 0.795 0.798 0.806 0.814 0.827 0.828
0.731 0.730 0.732 0.737 0.748 0.759 0.771 0.774
0.795 0.794 0.793 0.798 0.807 0.817 0.826 0.831
0.797 0.796 0.796 0.800 0.809 0.820 0.824 0.831
0.863 0.858 0.856 0.859 0.866 0.873 0.883 0.890
0.892 0.888 0.887 0.887 0.895 0.904 0.914 0.923
30.052 0.054 0.049 0.048 0.047 0.044 0.038 0.029 0.034 0.034 0.045 0.056 0.070
29.878 0.879 0.877 0.874 0.872 0.869 0.867 0.868 0.875 0.883 0.894 0.901

29.898 0.899 0.896 0.892

0.894 0.932

0.906

10h

Mean Mean max. min.

Noon. 1 p. m.

1

:

0.021
0.999 0.981 0.971 0.968 0.970 0.968 0.974 0.981 0.986 0.992 0.984 0.048 0.930
0.035 0.020 0.002 0.985 0.977 0.972 0.968 0.972 0.78 0.981 0.988 0.998 0.062 0.935
1
0.903 0.895 0.881 0.867 0.857 0.850 0.845 0.847 0.852 0.864 0.839 0.872 0.922 0.820
0.870 0.864 0.856 0.847 0.837 0.831 0.828 0.827 0.829 0.842 0.851 0.846 0.893 0.798
0.875 0.869 0.861 0.855 0.846 0.838 0.833 0.830 0.832 0.840 0.852 0.854 0.901 0.809
0.828 0.824 0.818 0.810 0.802 0.794 0.786 0.783 0.787 0.793 0.804 0.807 0.846 0.765
0.775 0.772 0.764 0.754 0.742 0.733 0.723 0.723 0.728 0.733 0.741 0.745 0.785 0.707
0.834 0.827 0.819 0.812 0.802 0.792 0.787 0.782 0.783 0.789 0.798 0.806 0.848 0.759
0.826 0.818 0.808 0.794 0.784 0.777 0.773 0.777 0.781 0.789 0.796 0.801 0.847 0.747
0.891 0.883 0.868 0.855 0.849 0.844 0.840 0.844 0.850 0.859 0.866 0.864 0.913 0.812
0.927 0.913 0.900 0.889 0.883 0.879 0.879 0.884 0.890 0.893 0.898 0.898 0.961 0.837
0.062 0.048 0.035 0.025 0.023 0.023 0.025 0.029 0.035 0.039 0.044 0.041
0.904 0.894 0.883 0.872 0.864 0.859 0.855 0.856 0.860 0.867 0.872 0.876

0.097 0.991

0.927 0.826

Mean Mean max. min.