Proceedings. 7 



I believe, far away in the North of Russia. During the recent 

 fogs its centre was very nearly over London, and the highest 

 pressure prevailed over our southern and midland counties, 

 where the fog was at its worst. But the anticyclone was a 

 gigantic one, and made itself unpleasantly felt in Ireland, to 

 right away over Germany ; and from Norway to the Bay of 

 Biscay and the Soiith of France. Throughout the whole of 

 tliat vast area fog prevailed. 



It should be borne in mind that fogs are caused by con- 

 densation arising from differences of temperature between the 

 earth's surface and the adjacent air. The earth's surface may 

 vary in temperature. Clay will probably be colder than sand ; 

 water will differ from the surrounding land, and so fog may 

 be different in degree in different places. The railway-cutting 

 through the clay from Forest Hill to New Cross, being a 

 sheltered place with a cold soil, is very subject to fog. 

 Again, London, with its great river, is the especial home of 

 fog. "Water is very slow to be influenced by changes of 

 temperature ; the sea attains its maximum temperature late 

 in the summer, and its minimum in the spring. Fogs 

 therefore frequently occur over water because the air is 

 often at a different temperature to the water. At Haslemere 

 a spring rises and flows in a still stream of about 80 ft. in 

 breadth, where it has been banked in, for a distance of about 

 100 yards. The temperature of the spring is about 40°, and 

 in sharp frost a mist is to be seen rising from its surface, 

 because the water retains an even temperature, — it never 

 freezes, — while the air has fallen more than 10° below it. 



The mention of London brings us to what is known as the 

 " London particular" fog. The gloomy, yellow-black fog that 

 gets into one's eyes and makes them smart, gets into the 

 mouth and gives a sulphurous taste, and gets onto the face 

 in unpleasant patches known as " blacks." The cause of this 

 variety is not far to seek. London, with its vast population 

 of people and horses, emits vast quantities of carbonic acid 

 gas. The numberless chimneys in belching out their smoke 

 emit a distillation of hydro-carbon vapour, and at the same 

 time a quantity of sulphurous acid. The vapour condenses 



