392 Transactions. — Miscellaneous. 



water there is a tendency to equality of temperature which 

 becomes coincident at certain depths, so the same tendency is 

 met with in the atmosphere, and apparently becomes coinci- 

 dent within the polar area. 



Air is but slightly heated by the passage of the sun's ravs 

 through it, but when the heat has reached the earth's surface 

 the air becomes heated by contact. It then expands, its 

 density is less, and, as a consequence, it rises. The direction 

 of the movement is either vertical or vertical with a hori- 

 zontal tendency, and just as the water movements are regu- 

 lated as to rate and direction by the differences or contrasts 

 in temperature, so the aerial movements are regulated in a 

 similar manner. The deep waters in the temperate and 

 frigid zones might be expected to move towards the warmer 

 areas exactly in accordance with the characteristic tempera- 

 tures of the waters of the ocean at all depths, just as was 

 shown must occur under the conditions named in the ex- 

 amples quoted. The vertical height of the snow-line dimin- 

 ishes as the polar region is reached, it being regulated by the 

 amount of surplus heat available in each zone. The tempera- 

 ture scale from the equator is a descending one between it 

 and the pole, whether that scale be taken on the surface or 

 at any elevation whatever above the surface. If the surplus 

 heat which is supplied to the different zones were to be 

 equalised by atmospheric distribution as it passes away by 

 radiation into space the same atmospheric temperatures 

 would result, but the very fact of there being atmospheric 

 differences of temperature at the same elevation in the several 

 zones shows that the heat-rays which are emitted from the 

 surface in each zone are mostly, and perhaps wholly, used in 

 the zone where such rays reach the earth. 



Scales of temperature can be drawn at any parallel of 

 latitude to represent a vertical and horizontal measure of heat, 

 but the alteration of temperature in the vertical scale is much 

 more rapid than in a horizontal one ; but this could not be 

 were the heat from tlie earth's surface conveyed by the 

 atmosphere in a horizontal rather than in a vertical direction 

 with a shghtly horizontal tendency. In connection with 

 these scales representing vertical and horizontal temperatures 

 it is needful to keep two things clearly in view — first, the 

 barometric pressure on the earth's surface may be said to be 

 the same for all degrees of temperature between the equator 

 and the polar area ; second, the pressure of the atmosphere 

 at freezing-point varies from the equator to the polar area 

 from 15 in. at the equator to 30 in. within the frigid zone — in 

 other words, freezing-point at the equator would be at 20,000 ft. 

 elevation and a barometric pressure of abqut 15 in., whilst 

 within the polar area freezing-point would be at sea-level, and 



