| Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
| 1901 | 40.5 | 38.3 | 44.4 | 59.9 | 68.9 | 72.6 | 71.5 | 63.4 | 52.2 | 44.8 | 34.3 | 53.4 | 53.4 |
| 1902 | 33.2 | 37.8 | 48.0 | 58.3 | 66.7 | 68.4 | 71.3 | 73.0 | 63.0 | 54.3 | 53.0 | 37.2 | 55.4 |
| 1903 | 36.2 | 40.5 | 50.3 | 52.8 | 59.2 | 61.1 | 68.6 | 70.5 | 59.0 | 50.3 | 41.1 | 32.9 | 52.0 |
| 1904 | 31.7 | 44.9 | 51.4 | 52.8 | 60.5 | 67.4 | 68.4 | 72.2 | 67.6 | 54.3 | 41.9 | 38.6 | 54.3 |
| 1905 | 33.1 | 31.9 | 53.1 | 55.7 | 66.3 | 70.9 | 69.3 | 17.5 | 66.6 | 55.6 | 50.3 | 32.0 | 54.8 |
| 1906 | 36.2 | 36.7 | 44.0 | 56.0 | 61.1 | 68.1 | 69.8 | 68.9 | 67.9 | 49.1 | 46.1 | 44.3 | 54.1 |
| 1907 | 40.5 | 57.9 | 51.2 | 58.7 | 68.4 | 71.3 | 71.2 | 65.7 | 57.6 | 42.1 | 40.9 | 57.0 | |
| 1908 | 38.4 | 39.7 | 56.5 | 59.1 | 63.5 | 70.2 | 70.0 | 70.6 | 65.1 | 48.5 | 45.0 | 42.8 | 55.8 |
| 1909 | 42.7 | 41.5 | 47.1 | 53.2 | 60.2 | 68.6 | 73.5 | 72.0 | 63.3 | 52.2 | 52.2 | 32.8 | 55.0 |
| 1910 | 38.5 | 37.1 | 48.7 | 51.0 | 60.3 | 66.7 | 70.5 | 72.5 | 65.8 | 53.8 | 46.0 | 55.7 | |
| 1911 | 45.6 | 49.0 | 49.5 | 56.3 | 58.9 | 69.9 | 71.6 | 71.9 | 69.9 | 56.3 | 41.1 | 38.2 | 56.6 |
| 1912 | 34.1 | 33.3 | 43.9 | 54.9 | 62.8 | 66.7 | 72.4 | 70.9 | 64.9 | 55.0 | 40.0 | 37.7 | 53.1 |
| 1913 | 38.9 | 36.1 | 43.3 | 50.8 | 60.3 | 66.3 | 71.0 | 69.6 | 64.2 | 53.1 | 52.7 | 40.2 | 54.0 |
| 1914 | 40.5 | 36.6 | 43.5 | 3.6 | 62.8 | 70.6 | 72.4 | 72.1 | 65.0 | 54.7 | 44.6 | 35.9 | 54.5 |
| 1915 | 33.7 | 40.6 | 37.5 | 51.1 | 62.9 | 70.8 | 70.6 | 69.2 | 66.2 | 53.6 | 46.5 | 38.1 | 53.5 |
| 1916 | 43.4 | 38.7 | 47.1 | 52.5 | 62.2 | 69.0 | 72.3 | 71.0 | 62.9 | 51.6 | 42.0 | 39.4 | 54.4 |
| 1917 | 41.7 | 39.9 | 46.1 | 52.2 | 55.1 | 67.3 | 74.2 | 70.4 | 63.7 | 46.8 | 38.5 | 35.0 | 52.6 |
| 1918 | 27.0 | 43.8 | 52.5 | 53.7 | 63.5 | 71.7 | 68.7 | 69.5 | 59.5 | 58.9 | 45.1 | 44.9 | 55.0 |
| 1919 | 36.1 | 39.7 | 47.8 | 52.6 | 59.6 | 66.6 | 70.8 | 71.2 | 66.7 | 64.8 | 47.9 | 30.7 | 54.6 |
| 1920 | 43.5 | 46.9 | 51.8 | 63.8 | 65.4 | 69.9 | 68.7 | 66.0 | 52.6 | 40.3 | 37.7 | 55.2 | |
| 1921 | 43.0 | 40.8 | 55.4 | 50.8 | 58.9 | 68.0 | 70.5 | 69.1 | 68.5 | 48.3 | 47.9 | 42.0 | 55.3 |
| 1922 | 36.7 | 45.8 | 45.4 | 54.6 | 62.4 | 67.8 | 68.8 | 68.1 | 63.7 | 48.5 | 45.2 | 43.7 | 54.3 |
| 1923 | 43.7 | 40.8 | 42.6 | 52.6 | 60.0 | 66.7 | 68.5 | 68.9 | 64.3 | 52.5 | 40.5 | 44.8 | 53.9 |
| 1924 | 30.8 | 37.9 | 41.1 | 52.1 | 55.9 | 68.1 | 66.9 | 68.9 | 62.3 | 53.1 | 45.7 | 38.5 | 51.8 |
| 1925 | 33.2 | 41.6 | 45.9 | 56.6 | 56.9 | 70.3 | 73.3 | 70.8 | 70.0 | 57.6 | 45.5 | 35.2 | 54.8 |
| 1926 | 36.8 | 43.2 | 42.5 | 51.3 | 59.9 | 67.1 | 70.1 | 71.6 | 69.6 | 60.8 | 42.8 | 41.6 | 54.8 |
| 1927 | 42.1 | 47.4 | 47.3 | 59.5 | 66.4 | 68.6 | 70.1 | 70.8 | 66.3 | 56.2 | 54.8 | 37.8 | 57.3 |
| 1928 | 38.2 | 41.0 | 47.4 | 49.9 | 59.5 | 68.1 | 71.1 | 71.3 | 62.9 | 58.3 | 44.3 | 37.1 | 54.2 |
| 1929 | 39.5 | 35.7 | 50.3 | 58.5 | 62.3 | 68.2 | 70.6 | 69.5 | 65.2 | 55.6 | 41.6 | 38.5 | 54.8 |
| 1930 | 33.1 | 47.3 | 43.5 | 56.1 | 63.9 | 66.1 | 70.7 | 70.2 | 66.3 | 54.1 | 45.6 | 35.9 | 54.4 |