356 



NATURE 



{Feb. 12, 1880 



torrent of heated water. In this case, the fog which is 

 seen to rise from the river is caused by the cold water 

 condensing the vapour of the warmer air above it, which 

 at the time happens to be near the point of saturation. 

 Similarly, the Mississippi, which flows directly from colder 

 into warmer latitudes, is often enveloped in mists or fogs. 

 On the other hand, when the waters of a river are con- 

 siderably warmer than the air over them, the vapour 

 rising from them is condensed into fog by the colder air 

 through which it ascends ; and in such cases the fog will 

 be the denser in proportion to the stillness of the air and 

 its nearness to the point of saturation. 



What have been called radiation fogs make their 

 appearance during calm clear nights when the air in 

 contact with the ground gets cooled by radiation, and 

 becoming thereby heavier necessarily flows downwards 

 in much the same way as water, towards the lowest 

 levels, and floods all the low-lying grounds, mingling 

 with and diffusing itself through the moister air of the 

 low grounds, and condensing its more abundant vapour 

 into fog. 



Still further in such calm cold weather as has been 

 prevalent for some weeks in the south of England, the 

 temperature of the land falls at a greatly more accelerated 

 rate than that of the sea. When this happens the inter- 

 change of light airs and light breezes which set in from 

 the sea landwards and vice versa along a considerable 

 extent of coast, mixes the colder with the warmer and 

 more humid air-currents, and thereby lays a thick 

 covering of fog over the surface. 



There is yet another fog of great significance in the 

 study of atmospheric circulation, which spreads over a 

 much wider extent than any of the other fogs referred to. 

 Tnis is the fog which is frequently found in the region of the 

 outskirts of the anticyclone, or rather in the debatable 

 region between the cyclone and the anticyclone. The most 

 probable explanation of it is that it arises from the diffusion 

 of the vapour brought up by the cyclone outwards and 

 through the colder and drier air of those parts of the 

 anticyclone contiguous to it, where it is condensed into 

 immense breadths of fog frequently stretching several 

 hundred miles in length. Much yet remains to be done 

 in instituting, even, an exact and systematic observation 

 of this important weather phenomenon from the results 

 of which we might hope to come at some knowledge of 

 its true meaning and its significance in forecasting 

 weather, particularly those changes of weather which 

 terminate long tracts of fine dry weather. 



N ow if we examine the weather charts from new year's 

 day to the present time, it is seen that the south-east of 

 England has been constantly either within anticyclones 

 or under their immediate influence, the centres of which 

 kept shifting to and fro over a rudely shaped quadrilateral 

 marked off by Corunna, Sligo, Copenhagen, and Bu- 

 charest. During nearly the whole of this time, London 

 has been within the belt of fog and mist which continu- 

 ously, or discontinuously, has been skirting the margin of 

 these anticyclones. At the same time the air has been 

 unusually calm. Thus at Greenwich for the four weeks 

 ending January 31, the mean daily horizontal movement 

 of the air was only 144 miles, being 182 miles less than 

 the average ; and during the five foggy days in the last 

 week of January the daily movement of the air was 269 

 miles under the average. 



Hence, then, the fogs which London has had in common 

 with the south of England and parts of the continent 

 opposite, have been intensified by the low temperatures 

 and still atmosphere bringing from time to time their con- 

 tributions of radiation fogs and other fogs, still denser, 

 drifting ever and anon through the heart of the city from 

 the adjoining sheets of salt and fresh water. The last 

 touch in the production of the very worst character of 

 these fogs was doubtless given by the smoke of London, 

 in the manner explained by Sir John Herschel in his 



'' Meteorology," whereby each particle of soot acting as an 

 insulated radiant, collects dew on itself, and sinks rapidly 

 down through the fog as a heavy body, thus giving to 

 these fogs their yellow thick consistency and the suffocat- 

 ing and unwholesome sensation experienced in breathing 

 them. 



In the weekly reports of the Registrar. General for 

 December, 1873, several deaths are certified as having 

 been more or less directly caused by the extraordinarily 

 dense fogs which then prevailed ; and in one of the reports 

 it is remarked that " In the large provincial towns, where 

 the same cold weather was unaccompanied by fog, the 

 increase in the mortality was slight compared with that 

 which occurred in London." In the last week of January, 

 when the fog was so dense, the deaths in London from 

 whooping-cough rose to 193, — a fatality from this disease 

 hitherto unexampled in the London bills of mortality. 

 A careful examination of the weather and health of 

 London, particularly as regards the deaths resulting from 

 throat and nervous complaints, could not fail to con- 

 tribute materially to the diffusion of a better knowledge 

 than we yet possess of the influence of these fogs on the 

 public health. 



NOTES 

 Dr. Broca, the eminent anthropologist, has been elected 

 a life member of the French Senate by a majority of eight. 

 This election has created some sensation, Dr. Broca's nomi- 

 nation having been opposed on the ground of his Darwinist 

 opinions. Dr. Broca opened the last meeting of the Anthropo- 

 logical Society by a short address, in which he considered his 

 election as a victory gained not only by his political, but alsoby 

 his scientific opinions. 



Almost a panic has occurred amongst the wine-growers of 

 Cape Colony, in consequence of the supposition that not only 

 was the Phylloxera causing the destruction of some of the choicest 

 vines, but that it had existed there, undetected, for several years. 

 An influential, and somewhat animated, meeting was held at 

 Cape Town to discuss the subject. We understand that samples 

 of the vines, supposed to have been attacked by the pest, were 

 forwarded to the Colonial Office and sent on to Kew, and that 

 these have been examined by Mr. McLachlan, who is of opinion 

 that all the characteristic signs of the action of Phylloxera are 

 absent, and that nothing is shown to induce uneasiness in the 

 minds of South African wine-growers on this score. The 

 samples had been packed in the wor.^t possible condition for 

 minute examination ; but according to a report in a Cape paper, 

 Mr. Roland Trimen, of Cape Town, had examined samples sub- 

 mitted to him on the spot, and pronounced a similar opinion. 

 Some of the vines are undoubtedly in an unhealthy condition, 

 from unexplained causes. It is to be hoped our Cape colonists 

 will not allow panic to take possession of them, and, under its 

 influence, rush into extremes. It is probable that some of the 

 South European nationalities that have carried the absurdity of 

 panic to its highest limit — to the extent of confiscating a bouquet 

 of w ild flowers in the hands of unsuspecting ramblers — unwittingly 

 permit the importation of " contraband " vines to a large extent. 



According to the report of the French Phylloxera Commis- 

 sion, the pernicious insect has spread in a deplorable manner 

 during the last two years, in spite of all measures to the con- 

 trary. The black patches on the maps of the Commission, and 

 which represent those districts over which the plague has a com- 

 plete hold, must be enlarged year after year. Great hope was 

 placed in snow, but it proved futile, inasmuch as snow must 

 cover the ground for at least forty-five days to destroy the 

 insects, and nowhere has the snow lasted so long as that. About 

 one-quarter of the French wine-growing districts are now de- 

 stroyed. All disinfectants prove useless, and it seems hopeless 



