The relation between general climatic conditions and the prevalence of
suicide has been somewhat exhaustively studied by students of
criminology, the result being a considerable accumulation of data and
the formulation of a number of more or less tenable theories. From
these studies we may safely conclude that the homicidal tendency, as
shown by self-destruction (suicide) and the destruction of others
(murder), is stronger in the temperate climatic zones than in the
torrid or frigid, and that in the late spring and early summer months
more of these offenses have been recorded than for any other period of
the year. To these few facts the seeming effects of cosmical forces
upon such tendencies has apparently been limited.
In fact, it was the oft-repeated statement that nothing was known of
the exact relations of the more definite meteorological conditions
with the prevalence of suicide--a statement to be found in most
treatises upon the subject--that has given rise to this paper.
Realizing that the science of climatology must include, and in fact be
based upon, a study of the meteorological conditions prevalent, and
that the study of these definite conditions for the exact times when
suicides or murders occurred might throw some light upon the question,
this problem was undertaken.
In the preparation of the accompanying charts, from the study of which
the conclusions herein stated were deduced, the record of crime for
Denver, Colorado, for the fourteen years ending with June, 1897, was
made use of. Superintendent Howe, chief of the city detective service,
has kept such a record with the greatest care, and we wish here to
acknowledge the many courtesies of his office.
No attempt has been made in this paper to compare the conditions for
Denver, either meteorological or social--and each is somewhat
unique--with such conditions elsewhere. In fact, such a comparative
study is at present impossible since data are wanting.
In the actual preparation of the charts each murder, suicide, or
attempt at suicide--which, for our purpose, is equally important--was
set down chronologically in the left-hand columns of large sheets of
paper ruled for the purpose. These sheets were then taken to the
office of the United States Weather Bureau, F. H. Brandenburg,
director, where were recorded in the proper columns the maximum and
minimum barometer readings, maximum and minimum temperature, maximum
and minimum humidity, maximum velocity of the wind, precipitation, and
character of the day for each day during the fourteen years on which
a crime of either class occurred. When several took place upon the
same day the fact was taken into consideration. From the sheets thus
filled out, the curves on the accompanying charts were plotted by
computing the per cent of crimes of each class committed under the
definite meteorological condition indicated.
The curves marked "normal" were constructed by tabulating in a similar
manner the conditions for every day in a sufficient number of days to
secure a fair average. Five years were so tabulated for Figs. 2, 3, 4,
and 5, and the records for nineteen years used in Figs. 1 and 6.
The whole number of suicides recorded is two hundred and sixty;
murders, one hundred and eighty. It may be noted that this number of
suicides, for a city averaging hardly one hundred thousand inhabitants
for the fourteen years, is largely in excess of the rate recorded for
American cities, but it must be remembered that some of these were
unsuccessful attempts, and also that the social conditions of Denver
tend to swell the number--containing, as it does, so many disappointed
in the last struggle for health.
[Illustration: FIG. 1.]
Fig. 1 shows the occurrence, in per cent, of crimes of both the
classes considered for each month of the year, together with the
monthly meteorological means, computed from the records for nineteen
years. The expectancy curve in the occurrence table is based upon the
supposition that the months of the year are all of the same length,
and that the numerical expectancy would be one twelfth, or eight and a
third per cent for each. It will be seen that the crime curves are for
the most part below the expectancy for the winter months, and above it
for the summer (except for April, and suicides for June), showing the
maximum for the latter class in May and for murders in March. Morselli
shows[C] that for most European countries suicides are at the maximum
in June, though a considerable number show that condition for the
later spring months. A study of the general meteorological means,
shown upon the same plate as the occurrence table, fails to indicate
any good reason for irregularity of the crime curves. The "month"
columns read from the top to the bottom of the chart, and by following
that for May, for instance, which month shows the maximum for suicide,
we find that the meteorological condition for each class of data is
about halfway between the extremes for that class for the year, while
for January (minimum suicides) each class is by far more divergent.
Yet a mean, like those considered in this table, is but the average of
the extremes, and those months which show great per cents of crime
also present great extremes of condition, which fact, interpreted in
the light of those disclosed by the charts yet to be considered, make
the occurrence curve more explicable.
[Footnote C: Suicide, International Science Series.]
[Illustration: FIG. 2.]
WIND.--An explanation of the various curves in Fig. 2 may serve for
the series following, so I give it somewhat in detail. The vertical
distances from the base line indicate per cents, and the distances
from left to right, divided into columns, the maximum velocity of the
wind per hour for the days tabulated. In the "normal" curve every day
for five years was considered, and it was found that seven per cent of
the days for that period showed a maximum velocity of between one and
ten miles (first column), forty-eight per cent a maximum velocity of
between ten and twenty miles (second column), nineteen per cent a
maximum velocity of between twenty and thirty miles, and so on, as
indicated by the curve. Now, it can readily be seen that this normal
curve may also be considered the expectancy curve--_if the wind has no
effect_. That is, if forty-eight per cent of the days of the year show
a maximum velocity of the wind, between ten and twenty miles an hour,
the law of probability would give us the same per cent of the crime
for the year on such days if this meteorological condition were not
effective.
What we do find, however, is indicated by the other curves, and any
increase of crime over expectancy may in this case be ascribed to the
wind. We notice that for slight velocities (one to twenty miles an
hour) the crime curves are below that of expectancy, but we can see
that if the sum of all the per cents for any one curve is one hundred,
and one is forced above the other at any part, there must be a
corresponding deficiency at some other part. So we may, perhaps, with
justice suppose that these mild velocities do not exert a positively
quieting effect emotionally, but simply a less stimulating effect than
the higher ones. For velocities of between twenty and thirty miles a
marked effect is noticeable, and under those conditions the proportion
of suicides to that expected is 37:29; velocities of from thirty to
forty miles, 14:11; of forty to fifty miles, 7:2; of fifty to sixty
miles, 0.4:2.6; of fifty to sixty miles, 0.2:2. The curve for murders
shows the increase to be slightly less than for suicides, but the same
general relation is preserved throughout. The value of such curves is,
of course, somewhat proportional to the number of observations made
and recorded, and we must confess that two hundred and sixty
(suicides) and one hundred and eighty (murders) is a hardly sufficient
number from which to deduce a definite law, but we can hardly doubt,
even considering this somewhat limited number, that the wind is, in
our problem, a factor of no mean importance.
[Illustration: FIG. 3.]
TEMPERATURE.--Fig. 3 is intended to show, in a similar manner, the
relation between expectancy curves, based upon conditions of
temperature, and the actual occurrence of the crimes in question. With
this class of data, as well as that for the barometric readings and
humidity (Figs. 4 and 5), both the maximum and minimum readings are
considered. This was done instead of taking the mean of both for the
day, since in many cases the latter might be quite normal, while one
or possibly both the former might exhibit marked peculiarities. All
the curves were constructed precisely as in the chart just considered,
and those marked "normal" are again the expectancy curves. An
inspection of the chart shows no marked discrepancies till we reach
the higher temperatures. For the lower the coincidence for all the
maximum and all the minimum curves is not exact, but somewhat similar.
When, however, we reach for the minimum curves, temperatures of from
40° to 50° and from 50° to 60°, which means that for the per cent of
days indicated, the temperature did not go below those points, the per
cent of crime exceeds that expected under the conditions in the
proportions of 22:16.5 and 24:18 (suicides), and 21:16.5 and 29:18
(murders).
The same general relation exists between the maximum curves, where it
is shown that for temperatures between 80° and 100° the actual crime
is about thirty-three per cent in excess of the expected.
These facts have their bearing upon the already noted statement that
the summer months show a preponderance of homicide.
[Illustration: FIG. 4.]
BAROMETER.--Fig. 4, disassociated from the others, shows but little.
Naturally we should not look for very marked effects from variations
of an inch or less in the barometric readings, when in the course of a
journey from the sea level to Denver a change of six inches is brought
about, and in going from the same point to the summit of Pike's Peak
one of nearly twelve inches without producing any marked emotional
abnormities, but we must take into consideration the fact that sudden
barometric variations generally accompany or more frequently precede
other important meteorological changes. In the latter case, though
they might be the primary cause of factors considered in this study,
they themselves would fail to show upon the tables.
[Illustration: FIG. 5.]
HUMIDITY.--This figure (Fig. 5) indicates in a very decisive manner
that states of low relative humidity, as shown by both maximum and
minimum readings, are conducive to excesses in both the classes of
crimes studied. For instance, for maximum humidities between ten and
twenty the proportion of actual crime to that expected is 1:0.1;
between twenty and thirty (suicide), 11:1; between thirty and forty,
9.5:4.5; between forty and fifty, 15:8. The maximum curves show
somewhat the same general relation though not with quite so marked
divergences. To one who has experienced the general low humidities of
our Colorado altitudes (Denver is one mile above the sea level) this
result is not surprising. There is no doubt that a nervous tension
much in excess of that common in the lower altitudes exists, due in
part, perhaps, to the deficiency in barometric pressure and a
consequent effect upon the respiratory processes, but probably, as
shown by these curves, more largely to the dryness of the atmosphere,
as indicated by low humidity. I hope at some future time to verify or
disprove this supposition by a comparative study made at some lower
altitude.
[Illustration: FIG. 6.]
CHARACTER OF THE DAY.[D]--Fig. 6 shows the relation between the
expectancy of crime, based upon the actual per cents of cloudy, partly
cloudy, and clear days (records of nineteen years), and its actual
occurrence. The disagreements are very slight, although a slight
excess of murders is shown for cloudy days.
[Footnote D: By the United States Weather Bureau days are
characterized as "cloudy" when for 0.8 or more of the possible
hours of sunshine the sun is obscured; "partly cloudy" when from
0.4 to 0.7 inclusive is obscured; and "clear" when 0.3 or less.]
SUMMARY.--Fig. 1 shows at a glance no generally prevailing
meteorological conditions to which can be ascribed, with any degree of
certainty, the monthly variations of crime.
Fig. 2 shows that high velocities of wind seem to increase to a marked
extent the tendency to crime. For the highest velocities increasing
the probability twenty times (two thousand per cent).
Fig. 3 shows that high temperatures seem to have the same effect, that
of between 90° and 100° increasing the probability one hundred per
cent.
Fig. 4 fails to show that barometric changes are accompanied by any
marked excesses in crime.
Fig. 5 shows that low conditions of relative humidity are attended
with very marked excesses, those below thirty increasing the
probability of suicides eleven times (eleven hundred per cent).
Fig. 6 fails to show that the character of the day has any
considerable effect.
Considering briefly, in conclusion, the results of the foregoing
study, and comparing them with a somewhat similar one for children,[E]
we may safely conclude that the tendency to homicide varies with those
meteorological conditions which bring about an emotional state
necessitating a considerable discharge of motor stimulus. The same
conditions which bring about irritability and unruliness on the part
of the child accompany suicidal tendencies.
[Footnote E: See The Child and the Weather, Pedagogical Seminary,
April, 1898.]
This supposition is upheld by the fact that suicide is less common in
the colder climates, where the metabolic processes are slow, and in
the torrid zone, where the heat produces a general depletion of energy
for motor discharge, than in the temperate regions, where the climate
is exhilarating. The study, from the social standpoint, too, leads us
to the same conclusion. The excess of crime in the social whirlpools
of our great cities is convincing, and especially the careful study
made by Morselli of the prevalence of suicide in the different
countries of Europe, interpreted in the light of what we know of their
social conditions.
Yet, in considering the facts disclosed by the present paper, we must
not dogmatically assert that each is of the importance that the
figures indicate. In fact, it seems evident from a careful study of
the sheets, which show all the conditions together for the same day--a
thing impossible with the charts illustrating this paper--that the
various conditions for the day mutually react and interact upon one
another, certain combinations seemingly resulting in a re-enforcement
of the tendency to crime, while certain others inhibit it. Space
forbids any full discussion of this phase of the problem in the
present paper, but it very probably will be made the subject of some
future study.
AUTHOR'S NOTE.--The above paper was written more than a year ago.
Since that time the work of comparing the prevalence of crime
with the meteorological conditions has been carried on upon a
much larger scale in the city of New York. An immensely greater
number of data have served to corroborate the earlier conclusions
arrived at in this Denver study, only in minor points--and those
directly traceable to the very different climates--proving at all
in opposition to them.--NEW YORK, _July, 1899_.