CLIMATE OF LONDON.
THE temperature of the air in the metropolis is raised by the artificial
sources of heat existing in it no less than two degrees on the annual mean above
that of its immediate vicinity. Mr. Howard, in his work on Climate, has
fully established this fact, by a comparison of a long series of observations
made at Plaistow, Stratford, and Tottenham Green (all within five miles of
London), with those made at the apartments of the Royal Society in London, and
periodically recorded in the Philosophical Transactions. In explanation,
Mr. Howard refers to the heat induced by the population (just as the temperature
of a hive of bees), and from the domestic fires, and from the foundries,
breweries, steam-engines, and other manufactories. "When we consider that
all these artificial sources of heat, with the exception of the domestic fires,
continue in lull operation throughout the summer, it should seem that the excess
of the London temperature must be still greater in June than it is in January,
but the fact is otherwise. The excess of the City temperature is greater in
winter, and at that period seems to belong entirely to the nights, which average
3.710º warmer than the country; while the heat of the days, owing, without
doubt, to the interception of a portion of the solar rays by a constant veil of
smoke, falls, on a mean of years, about a third of a degree short of that in the
In the winter of 1835, Mr. W.H. White ascertained the temperature in time City to be 3º higher than three miles south of London Bridge; and after the gas had been lighted in the city four or five hours, the temperature increased full 3º, thus making 6º difference in the three miles.
Dr. Prout found that when his observations were made during the prevalence of wind (his station being at time western extremity of London), the air blowing from the east contained a minute portion of oxygen less than that which blew from the west. The difference was exceedingly small; still, it tended to show that the air which has passed over the busy streets of the metropolis differs in its amount, not only of carbonic, acid, but also of oxygen, from the air which has not reached those scenes.
Change of air in the metropolis is mostly effected by the mixture of the gases composing it. There are hundreds of places in London into which the wind never finds admission; and even among the wider streets there are many through which a free current is rarely blown. It is only in the night, when combustion in some measure ceases, and the whole surface of time earth is cooled, that the gases are gradually removed, and time whole atmosphere of the City is brought nearly to an equality. Nothing, indeed, can be more striking than the difference even in the sensible qualities of the air of London in the early morning and in the evening: in the former it has a coolness amid refreshing clearness, which those who know it in time heat of later hour can scarcely imagine.
Every one line observed upon dirty windows in the metropolis small tree-like crystalizations : these consist of sulphate of ammonia, which is produced in the atmosphere by the burning of vast quantities of coal, combining with the sulphurous acid in the atmosphere.
Owing to the smoke, many species of flowers (the yellow rose, for instance), will not bloom within ten miles of London; Paris, on the contrary (where wood is almost universally burnt), produces the finest flowers, not alone in the gardens of the Tuileries and Luxembourg, but in the nursery-grounds of the famous rose-growers, Noisette and Laffay; which, in the Faubourg St. Germain, enjoy advantages such as it would be necessary to retreat some miles from London to secure.
In London, in sunny weather, some fine effects of light and shade may be witnessed in the neighbourhood of the public buildings. Miss Landon refers to a bright day in spring as "a very spendthrift of sunshine, when the darkest alley in London wins a golden glimpse, and the eternal mist around St. Paul's turns to a glittering haze."
John Timbs, Curiosities of London, 1867