Light, Air, and Fog. by G

13 LIGHT, AIR, AND FOG. BY G. V. POORE, M.D., F.R.C.P. Read at the Sessional Meeting, February 8th, 1893. IN considering the climatological conditions which are favourable to the formation of fog in London one cannot do better than examine actual facts; and, therefore, I have recourse to the returns to the Registrar-General for the week ending December 26th, 1891, for the purpose of making a critical study of the notable fog of Christmas, 18i)1, its cause and consequences. In order that fog may be formed, the air must be laden with moistu1’e, and consequently in London the winds which bring the fog are those which come from the eastward, over the sea and up the estuary of the Thames. Fogs are necessarily phenomena which depend upon stillness of the air, for they are quickly dissipated by even a moderate breeze. In order that the moisture-laden air may precipitate its moisture in tlie form of fog it needs to be c7ailled, and, therefore, our winter fogs only occur in cold weather. December 20th, 1891, at Greenwich was a clear frosty day with very light air from the north-east. On the following day the wind became due east and dropped to a dead calm, and then commenced a dense fog which continued till the evening of Christmas Day, when the wind shifted to the south-west and the frost and fog came to an end. In the week ending December 26th six days were frosty, and a dense fog continued for the greater part of five days. The air was almost saturated with moisture. The mean daily value of temperature was 10.2 degrees below the average, and amounted to 29.1 degrees only. Out of fifty-four hours during which the sun was above the horizon, sunshine was registered at Greenwich during 4.7 hours only, and the sum of the horizontal movement of the air for the week amounted to 784 miles, or 1,341 miles below the averaged. The barometer stood at 30-49 inches at the beginning of the week and gradually fell to 29~7 at its close. These quantities are, be it remembered, the result of observations at Greenwich, and taken about 150 feet above the mean sea-level. Meteoro- logical observations in the centre of London are not recorded with any systematic care, but we may feel tolerably sure that the temperature in London was slightly higher than at Downloaded from rsh.sagepub.com at WESTERN OREGON UNIVERSITY on June 1, 2015 14 Greenwich ; that even less sunshine was recorded, and that the rate of movement of the air was even less and amounted to downright stagnation. The characteristics of the air during a fog are, then, clark7zesq, coldness, cw:mpness, and stagnation. It appears probable (although I know of no exact observations) that the mobility of the air and the diffusibility of its component gases is diminished during a fog. One of the often-recorded phenomena of a fog is the way in which it remains stationar,y in banks, and with exact limits (forming real pillars of cloud), for hours at a time; and one must take it for granted that the products of respiration and combustion are not easily removed in such circumstances, but remain to irritate, and perhaps to poison, t.hose who are surrounded by such envelopes of vapour. It is this stagnation of the air which, I believe, constitutes one of the great dangers of a fog. In estimating the effect that a fog has upon the health and comfort of those who are Immersed in it, a very important matter is its duration. All fogs, and especially London fogs, which are laden with irritative and infective particles, are very trying to sufferers from lung disease, especially those afflicted with chronic bronchitis, and the danger to these persons may be looked upon as proportioned to the length of time they are exposed to adverse circumstances. If the fog, after a few hour’s duration, clears up, the lungs get rid of the irritating matter, respiration becomes normal again, and the patient is able to withstand a second bout of fog when it returns; but if a fog continues for a few days instead of a few hours, there is no respite, and the patient succumbs. I have elsewhere compared Londoners in a fog to fish in a bowl, who suffer from the neglect of their owner to change the water; and it is evident that the longer the clange be delayed, the more unfitted the water becomes for the respiration of the fish, and the greater is the danger. So the danger of a fog increases with its duration, for not only do the dwellers in it get no respite with which to obtain, as it were, a new lease of life by even a few gasps in the fresh air; but the dense fog-bank which weighs upon them gets hourly fouler and fouler from the products of combustion and the smoke (a result of non-combustion) from thousands of chimneys and the respiratory and other impurities from millions of men and animals. A very note- worthy feature of the fog of Christmas, 1891, was its duration: it began on Alonday evening, and lasted, in a very dense form and without intermission, until Friday night; so that the time during which the Londoners had to endure this weather this mixture of coldness, dampness, foulness, and stagnation- was close upon a hundred hours. Downloaded from rsh.sagepub.com at WESTERN OREGON UNIVERSITY on June 1, 2015 15 When we come to consider what effect this long-continued fog had upon the health of London we find that we have many facts to take into consideration before we can arrive at any conclusion. The effect of cold and fog upon the death-rate is produced almost immediately because there is always a large number of sufferers from chronic maladies who are ripe for departure so soon as the first adverse circumstance arrives to overtax their feeble powers. Of course there are many others who do not die at once, but whose condition is so aggravated by the fog that they succumb in a few weeks or so. When fog and cold set in on a Monday some of the results of it would certainly appear in the death-returns furnished to the Registrar-General on the following Saturday night, but, as in this particular week Christmas Day fell upon a Friday, the work of Registration was upset, and many of the deaths occurring in the week, ending December 26th, were not registered until the following week, ending January 2nd. It thus follows that in order to estimate the effects of the fog we must take the deaths occurring in the fortnight, ending January 2nd, and in this way we eliminate the distur bing influence of Christmas. The estimated average number of deaths for the weeks ending December 2Gth, 1891, and January 2nd, 1892, respectively, is stated by the Registrar-General to be 1,813 and 1,915, giving a total of 3,728 for the fortnight. The actual number of deaths registered in these two weeks was 1,771 and 3,399, giving a total of 5,170 for the fortnight, or an excess of 1,442. The excess of actual deaths in the week ending January 2nd, over the calculated average was 1,484, so that we may, in considering the details of the excess for the fortnight, limit our attention to the second week alone. To do so will save much trouble, and will not materially influence our conclusions. The death-rate for the fortnight averaged 32, and for the two weeks respectively, it was Z1~9 and 42. Limiting our attention to the second of the two weeks, we find the following causes of death show a marked excess over the Excess. averages - Downloaded from rsh.sagepub.com at WESTERN OREGON UNIVERSITY on June 1, 2015 16 It is noticeable that the excess of deaths is mainly attribut- able to lung diseases or zymotic diseases, such as whooping- cough and measles, in which lung complications are very common. Deaths from circulatory disease were also far above the average, but as anything which hampers the action of the lungs must exercise a baneful influence on the circulation, this is what one would naturally expect, and merely tends to strengthen the assertion that cold and fog kill primarily by their effect on the lungs. The death-rate for the whole of London was 42, while the death-rates for the several districts were as follows : - It is noticeable that the western district suffered more than the northern or the southern, which is not to be wondered at, for with the slight airs from the East which prevailed the western districts would get the full effect of the foulness which drifted from the whole of the metr opolis lying to the eastward. The highest fog death-rate was in the central district. The high mortality caused by this fog was followed by a severe epidemic of influenza which lasted for six weeks, and the question naturally arises as to whether much of the mor- talit.y, apparently due to the fog, was not in reality caused by lllflLlenZa. This does not seem probable, because in the week ending January 2nd, there were not more than 37 deaths from influenza recorded in London. On the other hand may it not be considered as probable that the stillness and torpidity of the atmosphere during the fog was favourable for the conveyance of the influenza poison and helped, as it were, in determining the severity and wide extent of the epidemic.

Load more