2 
LECTURE ON CLIMATE. 
matter of climate itself. J have already given a 
definition of the term climate ; we have first to 
notice the atmosphere itself, and in connection 
with its changes, the instruments used to obtain 
the valuable results of such information. At- 
mospheric air, as viewed by the chemist, is a mix- 
ture (not a chemical compound) of 2 1 parts by 
measure of oxygen, 79 of nitrogen (or azote), 
and a trace of carbonic acid. Bub to the meteo- 
rologist it is the gaseous ocean under which we 
live, and to whose waves those of the most tem- 
pestuous sea are, by comparison, calm and insig- 
nificant. The ancients had long observed that 
space was filled by some material substance, and 
that on the removal of a body, air rushed in and 
filled the space ; hence the dogma that “ nature 
abhors a vacuum but it was reserved for Torri- 
celli, in the middle of the seventeenth century, 
to demonstrate the weight and pressure of air. 
He had noticed that in the pump a column of water 
was sustained of 32 feet, and argued, if a body 
heavier than water were used a column propor- 
tionately lower could only be sustained by the same 
Dower. To prove this, he took the heaviest fluid 
le could get— mercury — and placing it in a long 
tube, closed at one end, placed his finger over the 
other end to prevent its escape, and plunged this 
open end into a vessel also containing mercury ; on 
removing his finger, he found the mercury fell, 
until, balanced by the pressure of the air, it 
stood, not like the column of water at 32 feet, 
but at a height at 30 inohes : and by this beau- 
tiful and simple experiment be invented the ba- 
rometer. This, like most discoveries of value, 
was rejected by the scientific men of the day, 
who still adhered to the dogma, that “ nature 
abhors a vacuum at last came the 
final proof ; if said one, the suspension 
of the column of mercury, be due to the weight 
of the air, let us ascend a mountain with this 
instrument, and as we leave air behind us, 
there must be less above us, and this di- 
minished weight of air ought to press less, and 
sustain a lower column of mercury. This at 
once was done, and as they toiled up Torricelli 
with delight beheld, as at each halting place 
they made a new observation, the column, 
standing lower and lower, and the truth of his 
new doctrine established for ever. Indeed, 
from that time — the proportion having once 
been ascertained — mountains and all accessible 
elevations have been measured, by noting the 
difference at which the column of mercury of 
the barometer stands at the base and at the 
summit. To determine, then, the weight, and 
to ascertain the pressure of the air, the ba- 
rometer is an instrument of the highest im- 
portance, and as changes in these points cor- 
respond closely with changes in the weather, 
an indispensable one in][assisting to determine 
the climate of a place. It is apart Trom my 
purpose to go minutely into a description of 
these changes, for the principle on which the 
barometer acts being well understood, a few 
plain rules and careful observation are the 
proper teachers. To determine the tempera- 
ture of the air and of evaporation, the tem- 
perature of the dew point, the elastic force of 
vapour, the weight of vapour in a cubic foot of 
air, the additional weight required to saturate 
a cubic foot of air, and the degree of humidity, 
an instrument, the wet and dry bulb ther- 
mometer, is used. It is very simple in con- 
struction, and easily managed, and unlike 
Daniel’s hygrometer, without expense. The 
wet and dry bulb thermometer is simply two 
ordinary thermometers, with small bulbs and 
very small bores, fixed side by side on a frame. 
The wet bulb being covered with a piece of 
thin muslin, some cotton passes from the bulb 
to a bottle of water fixed below it. The read - 
ings of the two being taken, the results above 
mentioned are obtained by calculations or from 
tables prepared for the purpose. But this 
simple little instrument, besides the above 
data, gives — as well remarked by Mr. Gl&isher, 
the Secretary of the British Meteorological 
Society — useful information in many cases in 
ordinary life, and might very generally 
be used with advantage. The simple 
inspection of the two thermometers 
will often afford a better criterion of tbe weather, 
and the probability of rain, than the barometer 
itself ; thus in summer, if the temperature of 
tbe air increase, and that of the dew point de- 
crease, it is an indication of very fine weather; 
on the contrary, if the temperature of both in- 
crease with the day in nearly equal proportion, 
rain will almost certainly follow, as the tempera- 
ture of the air. Jails with the declining sun. 
Again, its importance to the requirements of a 
sick chamber are scarcely to be over-rated, as 
the comfort of the patient is often dependent, not 
so much on the temperature as on the hygrorae- 
tric condition of the air ; a difference of from six 
to eight degrees, between tbe reading of the two 
thermometers, will generally be found to give a 
pleasant degree of humidity ; if the air be too 
dry, it will be necessary to expose water, in some 
shallow vessel, of some extent of surface, so that 
the evaporation arising from it, mixing with the 
air, shall create a greater degree of humidity ; if 
on the contrary the air should be too moist, the 
required dryness may be obtained, either by rais- 
ing the temperature, or by placing in tbe room 
sulphuric acid, or any other medium which has 
the property of rapidly absorbing all watery 
vapour. For the same reason — the securing a 
healthy degree of humidity of the air, — this little 
instrument may render most essential service in 
the hot-house, green-house, and conservatory, and 
its careful use would result in the preservation of 
rare and valuable plants. 
In the consideration of this subject of climate, 
a most important point is that of the rainfall, 
and along with this, as intimately connected with 
it, the formation of clouds, deposit of dew, amount 
of evaporation, and prevailing winds. “When 
(says Lardner) condensation of vapour takes 
place in the upper strata of the atmosphere, a 
