November 5, iSgi] 



NA TURE 



13 



to have become much more frequent of late years, and, 

 in fact, it is doubtful whether in former times it ever 

 occurred. The immediate cause of this new form of fog 

 is difficult to explain. 



London has always been the head quarters of town 

 fogs, but now all the large towns appear to be emulating 

 it in this respect, and this is what we must expect ; an 

 increase of population means an increase of combustion 

 of coal, and that implies a pouring into the atmosphere 

 of more and more carbon, hydrocarbons, and sulphuric 

 acid. In dry and windy weather all these bodies may be 

 scattered so as not to produce appreciable effects ; but 

 let the air be still, and even approach a state of aqueous 

 saturation — then, we have seen, every particle of dust and 

 dirt becomes a centre for moisture to deposit on, and we 

 shall have a fog imprisoning all impurities and offering 

 them to us for inhalation. To burn coal so that only 



ascertain how far such views were correct, I studied the 

 Registrar-General's reports for the times of fogs ; but, as 

 I found it difficult to interpret the figures, I have ex- 

 pressed them by the curves upon these somewhat lengthy 

 diagrams (Figs, i, 2, and 3). I have selected times of 

 fog, viz. the winters of 1879-80, 1889-90, and 1890-91, 

 and have represented graphically the temperature, the 

 amount of fog, and the death-rate for each day. 



The results are, I think, worthy of careful study. The 

 first thing we learn from these diagrams is that by far the 

 greater number of fogs occur when there is a great fall of 

 temperature ; and clearly this is closely followed after a few 

 days by a great increase in the death-rate ; but how much 

 of this increase is to be attributed to the fog and how 

 much to the fall in temperature may be difficult to deter- 

 mine ; but we have evidence that when fogs occur with- 

 out fall of temperature they do not appear to be followed 



E.vJ>lanation of Diagrams.— T\ie. amount of fog is represented by the small 

 dark patches, the denser the fog the deeper the patch ; thus the Registrar- 

 General reports that it is either haze, foggy, fog, thick fog, or dense fog. 

 These different degrees of fog are represented by the vertical thickness : thus 

 dense fog is 5 times as deep as haze, and so with the other designations. 



The horizontal line represents the average temperature for each day for 

 the previous 20 years, and also the average weekly death-rate from diseases 

 of the respiratory organs for the previous 20 years. 



The curved line represents the divergence of temperature from the daily 

 average, and the shaded part the divergence of the death-rate from the 

 average. 



Scale : ,'0 inch represents i day, 1° F., and 10 deaths. 



1879 - 1880 

 'OCTI MOV I dec: JAN 



5 - II 12-1819-2526- I2 - 8 9-1516-2223-29 30-617- 13 14-20 21-27 2G -3 4- 10 



I..., 



I^dl 



III I F 



.1. 



^v|-y ^^ 



Fig. 



products of complete combustion shall escape is a 

 problem of much difficulty, and is comparatively rarely 

 done. Certainly the domestic fireplace does not do it, 

 but, on the contrary, is the principal cause of the dark 

 colour of our fogs. Many manufacturers, however, 

 liberally contribute to produce the same effect. 



I turn now from the constitution and production of fog to 

 note some of the effects it produces. First, with regard to 

 health, details on this point J leave to those who are 

 more able to describe them than I am, but I have a few 

 words to say with regard to the effect of London fogs on 

 the death-rate in general. There are many people who 

 feel so strongly the unpleasantness of fog that it induces 

 them to magnify its results, and make e.xtraordinary state- 

 ments with regard to the mortality it produces. It has 

 even by some been likened in deadliness to the Great 

 Plague of London, and to other great epidemics. To 



NO. 1149, VOL. 45] 



by any remarkable increase of death-rate ; for, on 

 December 15, 1889, there was a dense fog, and the 

 temperature was even above the average : under these 

 conditions the death-rate remained far below the average. 

 On December 13 and 14 in the same year, again, there 

 is a dense fog, an average temperature, and only an 

 average death-rate ; and the same thing happens on 

 February 4 in 1890, when, notwithstanding a dense 

 fog, the death-rate remained remarkably low ; and last 

 winter, on November 13 and 14, there was again a dense 

 fog, a high temperature, and an average death-rate. 

 With these four exceptions depression of temperature 

 goes with fog. There is no case of depression of tempera- 

 ture not followed by increase of death-rate. 



That many people suffer much, both physically and 

 mentally, from the effects of fog, there can be no doubt ; 

 but, as far as I can interpret these returns of the Registrar- 



