November 5, 1891] 



NA TURE 



There is still another action of town fogs, and one 

 which I believe is of great importance. I mean its 

 power of absorbing light. This power of abstracting 

 light depends principally on the amount of coal products 

 which the fog contains. The slower-vibrating red rays 

 can struggle through a fog which is absolutely impervious 

 to the more refrangible ones. Even a mist but slightly 

 tinged with smoke is opaque to the blue rays, and thus 

 screens us from their action but as Aitken has lately 

 shown, the heat rays can pass readily through. This 

 opacity of town fog to light is, I believe, one of its most 

 serious and detrimental characters. Animals can no 

 more thrive in semi-darkness than can plants ; and, im- 

 portant as the red rays may be, still it is undoubtedly the 

 blue rays which are most active in producing the prin- 

 cipal chemical charges going on around us. Experiments 

 lately made have strongly impressed me with the 

 wonderful activity which light confers on a mixture of 

 air and moisture, oxidations which in dullness and 

 darkness are impossible are easily and rapidly effected 

 by aid of a gleam of sunshine, or even a bright dif- 

 fused light. It is not possible, I believe, for people to 

 remain healthy where this source of chemical activity is 

 cut off, or even seriously diminished. In addition to the 

 loss of physical energy, mental depression is induced 

 by the absence of light, the whole tone of the system 

 becomes lowered, and may be a prey to actions which, 

 under brighter conditions, it would have been able to 

 resist. 



There is another action of light which is potent for 

 good. I mean its destructive action on many forms of 

 bacteria. Prof. Koch, at the last meeting of this Con- 

 gress, pointed out how his tubercle bacilli are killed by 

 even a short exposure to sunlight, and it is now well 

 established how inimical light is to the growth and 

 development of most kinds of bacteria. I wish I could 

 show you in some perspicuous way the enormous power 

 which town fog has of absorbing light, and bring forcibly 

 before you the great difference which exists between the 

 amount of light which reaches the inhabitants and build- 

 ings of a town, as compared to the amount on an equal 

 area free from smoke. A simple actinometer is much 

 required, and I hope the want will soon be supplied ; but 

 at present the only records bearing on this point are the 

 observations of direct sunshine made at various stations, 

 by the Meteorological Society and Meteorological Office, 

 with the Campbell-Stokes instrument, and some interest- 

 ing observations, by Mr. H. Raffles, on the distance at 

 which objects were visible during a London winter. 

 First, with regard to the sunshine experiments. One 



Hours of Sunshine during thu Year 1890. 



Station is situated in the heart of the City, in Bunhill Row, 

 and it is of much interest to compare the amount of 

 NO. I 149, VOL. 45] 



sunshine there with, first, the amount in the immediate 

 neighbourhood of London, where we are not beyond the 

 effect of town fogs, viz. at Greenwich on one side, and 

 Kew on the other, and also with a place not far from 

 London, which is beyond the influence of its smoke, 

 viz. Apsley Guise, near Woburn. I have also noted the 

 results obtained at Eastbourne, which is about as far 

 distant from London as Apsley Guise,.butin the opposite 

 direction, and is one of the sunniest places in England. 



Taking the totals of last year, the table shows that the 

 hours of sunshine registered at Bunhill Row were 1158, 

 at Greenwich 1255, at Kew 1405, at Apsley Guise 1420, 

 and at Eastbourne 1724 ; but for our present purpose we 

 must compare the amounts of sunshine at these places 

 duringthe wintermonths— November, December, January, 

 and February— and we find that at Bunhill Row there 

 were 95-8, Greenwich 150, Kew 171-7, Apsley Guise 205-9, 

 and at Eastbourne 2683 hours of sunshine ; that is, if 

 Apsley Guise be taken as giving the normal amount, 

 Bunhill Row received only half its due amount, and at 

 Eastbourne there was nearly three times as much sun- 

 shine as in the City. Now, on comparing the two other - 

 periods of 4 months, which are comparatively free from 

 fogs, the amount of sunshine is far more nearly the same 

 at all stations. 



Buahill 

 Row. 



March till June 

 July till October 



•1 542-4 

 ' 519-3 



Green- | jr Aspley East- 



wich. ! Gu.se. ■ bourne. 



581-4 619-4 I 581-1 

 5238 613-5 : 632-5 



7368 

 718-5 



Mr. Raffles, during the winter of 1887-88, which it 

 should ht noted was remarkably free from fogs, made a 

 series of observations of the distances to which he could 

 see from Primrose Hill, and found that looking south on 

 the 152 consecutive days from November to March, only 

 on 78 days could he see a quarter of a mile, and only on 

 83 days could he see to the same distance in a south- 

 westerly direction : this conveys a good idea of the opacity 

 of our London atmosphere. 



We attempt to compensate for the darkness which 

 fogs cause by the use of artificial light, and I have again 

 to thank my friend Mr. Livesey for the information he 

 has given me with regard to the extra quantity of gas 

 burnt in London during a day of fog. He tells me that 

 if a dense fog covered the whole of London, and lasted 

 all day, the additional amount of gas consumed would be 

 30 million cubic feet ; but since so extensive a fog as this 

 probably never exists, and certainly never lasts all day, 

 the actual amount consumed may be correctly reckoned 

 at 25 million cubic feet ; and if the cost of this be calcu- 

 lated at 2s. 6d. per 1000 cubic feet, which is rather below 

 than above the actual cost, it amounts to ^3 125 ; but after 

 all, it is not the single days of dense fog that measure the 

 extra amount and cost of artificial light used on account 

 of fog — it is rather the continually occurring dull days and 

 local transitory fogs which demand an e.xtra supply of 

 gas, and this is often 5 to 15 million cubic feet in a day, 

 and gives a total by the end of the winter which is very 

 considerable. As a standard of coinparison, I should 

 state that the total consumption of gas in the London 

 district in a day of 24 hours, during the depth of winter, 

 is 140 million cubic feet. 



Such, then, is an imperfect outline of the chief features 

 and effects of town fogs ; and now what is to be said with 

 regard to the possibility of getting rid of such fogs .'' This 

 question, it seems to me, resolves itself into this : fogs 

 cannot be prevented from forming over towns ; there are, 

 and probably ever will be, special inducements, in the way 

 of dust particles and products of combustion, for fogs to 

 form there ; but whether they must always be dark in 



