TRANSACTIONS OF THE SECTIONS. 35 
month of January, the temperature is comparatively high over the sea in that part 
of the Atlantic ocean that lies between these continents. But does this difference 
correspond with the relative extents of land and water in such a way as to indicate 
that they have the relation to each other of cause and effect? The northern Pacific 
ocean is about twice as broad as the northern Atlantic, up to,the latitude of above 50°, 
but the former is not proportionately warmer than the latter. Itis, on the contrary, 
colder; as may be seen from the isothermal lines over the two seas and adjoining 
parts, the temperature that is found at about 58° of latitude in the Pacific being 
carried as high as about 70° in the Atlantic. 
If the breadth of the sea produced the effect under consideration, the isothermal 
lines would be at the same height in the same latitudes over the land on each side of 
the sea; but it is well known that they are not. It is true the isothermals rise in 
the winter from Siberia to the middle of the Pacific ocean, showing that the water 
is there warmer than the land; but they rise still higher as they approach the Ame- 
rican coast, and attain the greatest height in that part near to or over the land in 
America; thus exhibiting the land in America, during the winter season, in the same 
latitude, much warmer than it is in Asia. In the Atlantic too the same isothermal, 
that on the American side is in the latitude of 42 or 44 degrees near Newfoundland, 
reaches 70 degrees on the European side near Norway; and that island is actually 
colder than Iceland, which touches the arctic circle in 66° of latitude. 
Professor Dove speaks of the Gulf-stream of the northern Atlantic as materially 
affecting the temperature of that locality up to a high latitude; but it is not shown 
to be the cause of the phenomenon under consideration. It is well known that the 
Gulf-stream is turned from its northerndirection off Newfoundland across the Atlantic 
towards Ireland and the Bay of Biscay, and is even thrown back on the coast of 
Africa. The frequent appearance of icebergs, far to the south in this ocean, indi- 
cates that an océanic current sets in here, not towards the north, but southward. It 
is known too, from attémpts that have been made to approach the north pole, that 
ἃ. cuitrent sets from the Polar sea near Spitsbergen to the south. It appears, there- 
fore, that the assumption that the Gulf-stream flows into a high latitude in this part, 
and warnis it, is not merely unwarranted, but at variance with known facts. 
But if neither the proportional extent of the surface of the sea, as compared with 
the land, nor the flow of a warm current of water carries high temperature to these 
northern latitudes, what is the cause of such temperature being found there? The 
answer to this question has been substantially given where I have pointed out the 
cause of all the great local heatings and winds that prevail over the globe. Buta 
reply is prepated by Professor Dove himself, where, in his remarks, he says, “ This 
surface,” meaning the surface of the globe, ‘‘being a highly varied one, the sun’s 
influence on it is also constantly varying, for the impinging solar heat is employed 
in raising the temperature of substances which do not change their condition of aggre- 
gation; but when engaged in causing the melting of ice, or the evaporation of water, 
it becomes latent. hen therefore the sun returning from its northern declination 
enters the southern signs, the increasing proportions of liquid surface upon which it 
shines causes a corresponding part of its heat to become latent, and hence arises the 
great periodical variation in the temperature of the globe which has been noticed 
above,” meaning the difference of temperature of the northern and southern he- 
mispheres. 
Why suppose that this effect of the evaporation of water is experienced only in 
the relative temperatures of the iorthern and southern hemispheres? And why not 
trace the effects of condensation of vapour, as well as of the evaporation of water? It 
is evident that heat is absorbed and made Jatent wherever vapour is produced, and it 
is equally clear that that heat is given out and made active wherever the vapour is 
condensed. 
It does not appear from the atmospheric currents which prevail that any portion 
of the vapour of the southern hemisphere passes into the northern to be condensed 
within or near to the basin of the Pacific, and there is no reason to suppose that it 
does; but in the basin of the Atlantic it is sufficiently evident that vapour does not 
so pass. The vapour which passes over the northern Atlantic, and is condensed 
beyond the British Islands and Norway, is supplied from the tropical and other seas 
north of the equator. The West Indies constitute the principal point of departure 
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