250
The above calculation has been made all through the months in which the population
has been below 850,000.
Object of compila
tion of Chart.
One of the ideas in compiling this chart was to check seme of the theories advanced
that temperature, humidity, wind, and clouds had a definite bearing on the daily mortality
of the city.
In reading the chart with a view to obtain a deduction of this kind 'from excessive
range of temperature, surplus clouds or other disturbing elements, a period of five days must
be taken as being the average number of days for the incubation of plague.
For example, on the 21st of November a cyclone occurred which gave a velocity of
wind of 27-23 miles per hour ; taking five days as the average length, of incubation, a high rate
of mortality might have been expected on the 26th November, but this was not the case.
Humidity.
Again, in studying the chart, it may be said that the line of humidity closely follows
the line of mortality, but this is merely a coincidence of plotting, as a glance at the humidity
and mortality lines previous to the first of November will show, and the scales are entirely
different.
Clouds.
Clouds, too, have been said to have a bearing on the death-rate ; the period extending
from the 15th to the 30th of December gives on some days a unit of eight of clouds (ten being
the maximum), which means nearly a wholly cloudy clay, while the other days average five ;
taking the average incubation period, it cannot be argued that clouds then had an adverse
bearing on the death-rate, as the deaths for the next week are less than the previous, and farther
examples of the same kind appear on looking more closely into the chart.
It would appear that a low temperature may have had an adverse bearing on the disease,
as through the months of December, January, and February, when the minimum temperature
was the lowest for the year, the mortality was greatest ; but on the other hand it must be
remembered that at this time few people slept in the open air as is their habit in warm weather;
the overcrowding in chawls and houses was therefore greater and the disease consequently
accentuated.
It is probable, however, that we must look even farther than the range of this chart for
the meteorological conditions having a possible bearing on the disease.
The mean annual temperature of last year was 80 . 07°, being the highest but one on
record for the last fifty years.
The total fall of rain for the year was 87 . 65 // ; this again is abnormal, being nearly 15"
above the average of the past fifty years.
These facts in themselves would, without further explanation, mean little, but it is
necessary to consider the details of this fall of rain.
June gave 28 . 02", being 8" above the average. July 36 . 44",° being 11 . 7" above the
average, August 20 . 8", being 7 . 5" above the average ; after the end of August only 1 . 61" of
lain was registered, 10" less than the average.
The above shows the serious and abnormal conditions of the period immediately pre-
ceding the advent of plague in the city and means that, with the moist and heated atmos-
phere of August, an unusual amount of evaporation was going on, drawing from a soil, water
and sewage-logged, exhalations which must·, of necessity, have had a distinctly adverse bearing
on the health of the town,