With regard to sustained, prolonged, or continued high temperatures during the summer months, for how many days have you known the temperature remain continuously at a high level ? This is a very important question, as it concerns infantile mortality in no small degree; I shall be grateful for your experience.
Much depends upon what temperature is deemed a "high level." If we assume that 90° and upwards is a high level, then such periods are very rare in Sydney; in fact during the past 24 years there have only been three. In 18G8 there were three consecutive hot days of which the mean temperature was 91.8°; in 1870 a period of four days with a mean temperature of 91.3°; and in 1874 a period of four days with a mean temperature of 90.2°. Since then, although sometimes near it, the temperature has never been for three days over 90°. Taking a lower level, we have one period of nine days in 1870, the longest on record, during which the mean temperature was 82.6°. It must, however, be distinctly understood that what is here taken is not the mean temperature of each 24 hours, but the highest temperature reached during the day, and which would not as a rule last more than three or four hours, if so much. If the mean temperature of the day were taken these temperatures, as given, would have to be reduced at least 10 per cent.
It is very unusual to have a hot period lasting more than three days; when it does happen it is generally in February or March. In the majority of cases high temperatures (over 90°) do not last more than one or two days. The exceptions generally occur in February or March, and have sometimes extended to four or five days. Hot weather, with a temperature of over 80° with a maximum of about 90°, has on a few occasions during the last 30 years extended from five to ten days; and in 1890, a memorable instance, to 12 days (the only case for 37 years).
The longest stretch of continuous heat noted was in January and February 1857. On January 28th, 29th, and 30th, the temperature exceeded 100°, and during the whole of February it was over 90° on 25 days, and above 100° on 12 days, the mean being 107°. In January 1858 there were 10 consecutive days over 90°, of which eight consecutive days were over 100°. In January 1860 there were in the beginning of the month seven consecutive days above 100° (maximum 107.5°). In the middle of the same month, seven days were over 90°, of which five exceeded 100°, two days reaching 113.7°. These are, however, exceptions to our usual experience. Although there are several other instances of great heat, yet the foregoing will suffice to show what we occasionally suffer without much harm being done.
During the period February 17th to February 23rd, 1891, the shade temperature at Townsville ranged between 81° and G2°, but at Cairns a range between 82° and 70° is of frequent occurrence, within at least fortnightly periods.