ON THE AIR AND WATER OF TOWNS. 21 
mometer, the rise of vapour and the perception of cold. If we ascend 
_ higher the same is seen on a larger scale—on miles instead of yards. A 
house may be in a clear atmosphere and the lawn before it in an impene- 
_ trable fog. One foot in height makes a difference, and one foot also of level 
_ distance, if the ground should differ in quality. The damper places give us 
a feeling of freshness, and cause also a slight irritation of the nose. Every 
wall causes a certain amount of dampness; and even in a windy day, a 
leafless hedge will protect one side from evaporation. In these respects 
therefore we may say truly, that every field or house in the country, as well 
as I believe every house in the town, has its own peculiar climate. 
The effect of wetness on the atmosphere of a town is very great; if we 
observe the smoke on a dry day we find that it rises, and if there be a little 
wind it is carried out in distinct black lines, leaving the air below compara- 
tively pure. Ifthe day be dull and wet, the smoke instead of being carried 
away is poured out directly into the streets, and a spectator at a short 
distance sees a basin of black fluid, if the town be in a valley, or a heap 
gradually diminishing towards the circumference as it falls into the adjacent 
country. It may be replied that the diffusion of gases would prevent this, 
_ but again it may simply be said that it does not prevent it. Besides, the 
_ smoke is not to be considered as a gas, the black portion is carbon and tar. 
If the carbon is wet, it becomes, like all other spongy bodies when filled 
with water, heavy, and of course falls down. The carbonic acid will no 
doubt be diffused more, but it also is strongly attracted by water, and must not 
be viewed as a pure gas, such as oxygen or nitrogen. Probably this is the 
reason of the very disagreeable state of our towns in damp gloomy weather ; 
_ it is such weather as does not allow the town to be ventilated. The same 
_ does not occur on a thoroughly wet day, when the matter is carried fairly 
_ down into the streets, and a certain freshness is perceived. 
Rain amidst smoke is just such a liquid as we might expect; it is a 
_ mixture of soot in a finely-divided, apparently dissolved state. It is how- 
_ ever not dissolved, and by boiling down may be got free. It is not easy 
to tell exactly the composition of the rain; for although I have examined 
_ it and obtained many products in it, so much may be ‘said to come from 
_ other sources when water is collected near houses or near the ground, that 
Ihave often suspected some source of error. However, I think if we take 
th hat rain which is collected on a very wet day, after many hours of continued 
en. This was collected frequently, and having obtained it so prea Iam 
Ww satisfied that the dust really comes down with the purest rain, and that 
simply coal ashes. No doubt this accounts for the quantity of sul- 
% Bcmionia of the sty coal, which is no doubt a valuable agent for neutral- 
zing the sulphuric acid so often formed. It must however be frequently 
_ acid with sulphuric acid, although I tare not found it so, as I have traced 
, fe xf streets to come to its source. The source however is not easily obtained, 
cause I believe it does not fall till at some distance. 
__ The rain-water at Manchester is about 24 degrees of hardness, harder in 
fact than the water from the neighbouring hills, which the town intends to use. 
ae can only arise from the ingredients obtained in the town atmosphere. 
__ But the most curious point is the fact that organic matter is never absent, 
although the rain be continued for whole days. This matter is capable of 
