428 JOURNAL OF THE PLYMOUTH INSTITUTION. 
and applied as power, would be capable of lifting each hour 
772 x 25 x 64 x 5,000,000,000,000 Ibs. through a height of 1 foot ; 
that is, of doing the work of steam-engines having an aggregate 
horse-power of 3,119,000,000,000, a power equal to that of nearly 
400,000,000 ships, such as our largest ironclads. Now when we 
remember that south-west Ireland and south-west England, and 
therefore Plymouth, are situate in the path of the Gulf Stream 
after its bifurcation, we can then see what influence our geo- 
graphical position must have on our climate. The effect of vapour 
in our atmosphere too in modifying temperature has been beauti- 
fully shown by Tyndall. He has proved that all perfumes, even 
from a bed of flowers, prevent in a great measure radiant heat from 
penetrating through the atmosphere laden with the perfume. 
Similarly he has shown that only a small percentage of radiant 
heat passes through vapour of water. Hence, on all sea-boards 
the vapour always found in the atmosphere, although invisible, 
acts as a screen to keep away the heat of the sun. This same 
screen, when the sun is set, or is hidden by clouds, also prevents 
radiation from the earth, and tends to keep on its surface what 
heat may have been absorbed by the soil-of which it is composed ; 
and thus vapour in the atmosphere secures a uniformity of tempera- 
ture. Most of us here know that a day’s jaunt on Dartmoor under 
a cloudless summer’s sun will burn our skins more than many days’ 
exposure on the sea under similar circumstances; and Tyndall, 
when ascending the Alps, says the heat from the sun was almost 
insupportable at the time he was hip-deep in snow. (Meteorological 
Lectures, p. 38.) The reason is to be sought for in what I have 
already said. Over the ocean the invisible vapour robs the sun of 
its scorching effects ; but on the Moor and on the Alps this vapour 
has been condensed and deposited in the form of dew, rain, or 
snow, and then the atmosphere is drier, and the consequence is the 
scorched skin to those who expose themselves. The effect of an 
atmosphere with little vapour in it, in allowing radiation to pass 
through it, has often been forced on my notice ; for it has frequently 
occurred that ice has been formed on the top of my house under a 
cloudless sky when the thermometers in the screen have not regis- 
tered below 35° F., or 3° F, above freezing. The material of which 
the screen is composed, the colour of the paint used, contiguity and 
direction of surrounding objects, character of the soil, and a count- 
less number of so-called trifles, tend to introduce discrepancies 
