Observations extending over three years on the amount of carbonic acid in the ground air in relation to the earth temperature at the depth of three feet with charts

Abstract

The connection between certain conditions of soil and the incidence of some infectious diseases has long been recognised by Physicians but the way in which these conditions operate has been variously explained.This paper shows a correspondence between the maximum of carbonic acid and the maximum reading of the earth thermometer at three feet. Late summer, when the temperature of the soil at three feet rose to the maximum,showed also the greatest amount of carbonic acid. Throughout the entire year much rain always produced a marked temporary increase in the amount of carbonic acid. These facts probably find their explanation in the increased bacterial life called into renewed activity by the heat and moisture.Moisture, as after much rain, may also act by mechanically sealing up the pores of the soil and thus preventing the normal escape of carbonic acid into the general atmosphere. The highest reading of the earth thermometer was towards the end of August when it ranged in the neighbourhood of 56° Fahr.Edinburgh is not what is known as a "Diarrhoea Town" that is, one in which that disease plays havoc with the infantile population in late summer and early autumn, but still, it is observed that most cases of infantile diarrhoea do occur at the time corresponding with the maximum reading of the earth thermometer at three feet, as is shown by reference to the Report of the Medical Officer of Health, Edinburgh 1898.The diurnal variation in the amount of carbonic acid showed an evening excess over the morning as the year approached near to the summer solstice and beyond it to the maximum reading of the year which occurred in the last days of August. After this period a morning excess over the evening was observed as the year approached near to the winter solstice and beyond it to the minimum reading of the year which took place in the end of March. During March, April and May, and again in September, October and November, the morning and evening variations were but little marked and temporary conditions of weather probably produced them. The year may be divided as regards the morning and evening variations in carbonic acid into four periods, September to December, December to March, March to June and June to September. In the first and third of these periods the morning reading is in excess,and in the second and fourth the evening reading.Any markedly high reading was always observed to follow a high rainfall. Excessively low readings on the other hand were observed after prolonged dry weather. A temporary increase after rain was constantly observed.The remarkable rise in the amount of carbonic acid in February and March of 1895 during the period of prolonged frost, and when snow lay on the ground for about a month, is not easy of explanation. The idea suggested itself that perhaps this was due to an increase of temperature in the soil caused by the covering of snow preventing radiation of heat from the upper layers of the soil. From observations made in February 1900 I found that such a covering of snow had no effect on the ground temperature thermometer whatever. The increase in carbonic acid may be explained to some extent by the sealing up of the surface of the soil thus preventing the natural escape of carbonic acid into the atmosphere. It was not observed that severe frost, apart from a covering of snow on the ground, was followed by increase in the amount of carbonic acid. In each of the three years the highest reading was observed towards the end of August.The remarkably low reading in October 1896 and again in August 1897 followed on a period of drought. No observation was taken from February to June 1897.Much rain was invariably followed by a marked increase in the amount of carbonic acid.No difference between the morning reading and the evening reading of the earth temperature at three feet was ever observed. The observations of the ground thermometer readings were taken on three alternate days of each week. The annual range of the temperature of the earth thermometer at three feet was about 20° Fahr. The lowest reading was observed to be in the month of February when it was in the neighbourhood of 36° Fahr. and the highest reading in the month of August when it was in the neighbourhood of 56° Fahr.There is observed to be a close correspondence between the annual curve of the earth thermometer and the annual curve of the amount of carbonic acid in the soil, that is, when the earth thermometer reading falls to the lowest annual point or rises to its highest annual point the amount of carbonic acid in the soil similarly approaches its lowest and highest points.It is further to be observed by reference to the Reports of the Medical Officer of Health, Edinburgh, that there was a close correspondence between the greater number of fatal cases of Infantile Diarrhoea and the highest reading of the earth thermometer at three feet.