Hawke's Bay Philosophical Institute. 719 



Huxley says that bacteria are killed by a temperature of 60° C. (140° Pahr.), 

 whilst they thrive best in a temperature of about SC^ C. (S6° Fahr.) ; 

 and the fact that fresh meat can be carried from New Zealand to Eng- 

 land in cool-chambers is a proof of the non-growth of bacteria in tempe- 

 ratures below freezing-point. Now, if we pursue this nebular theory so 

 far as it relates to the earth, it is evident that the air must have cooled 

 first. It is the outer envelope of the earth, and no heat could pass from 

 the earth as a body into space without passing througli the air. Heat can 

 only pass from a hot medium to one less hoc, and whatever heat the 

 earth has lost in the course of time must have passed into space through 

 the atmosphere as a medium. But we find at the present time thab 

 there are large areas of the earth, including land- and water-areas, so cold 

 that they are much below the temperature of freezing-point the year 

 round. And yet the cold, even in such places as are to be found within 

 the Frigid Zones, cannot be as intense as the cold to be found in the upper 

 parts of the atmosphere. But the true zonal region of cold is curiously 

 distributed over the earth. In the Torrid Zone a spot is reached in 

 vertical space known as the snow-line ; a similar spot can be reached in 

 diminishing elevations from the equator to the poles ; in fact, the snow- 

 line, as Nausen has pointed out with respect to the glaciers of Greenland, 

 is at the sea-level not far from the Arctic Circle. Little is known with re- 

 spect to the condition of the Antarctic Zone ; but Captains Cook and Wilkes, 

 as also Sir James Ross, report the existence of an immense ice-barrier 

 in that zone, which the late Professor Croll estimated to be some twelve 

 miiles in thickness (see ' Climate and Time '). Here, then, we find barriers 

 of cold in vertical space overshadowing land and water, and diminishing 

 in height from the equator to the Arctic and Antarctic Circles ; barriers 

 of cold in the Frigid Zone ; and, curious as it may appear, there is a cold- 

 communicating area in the lower depths of the ocean, linking together, as 

 it were, the cold areas of the north and south polar regions. Near the 

 Arctic Circle, at a depth of 1,400 fathoms, the water was found to be 

 32^° Fahr., while in the Red and Arabian Seas, at a depth varying from 

 1,400 to 1,800 fathoms, the temperature was only 33-i°. Thus there are 

 cold barriers now surrounding the earth in every direction, which circum- 

 scribe the limits of inhabitability, if not of all animal and vegetable life, 

 certainly of ail the higher forms ; and this circumscribed area, try how we 

 may to avoid it, is slowly but surely becoming more circumscribed by 

 reason of the loss of terrestrial heat that is slowl}' going on. Here, then, 

 we see prospects of the coming time in the history of the earth as a planet, 

 when the cold will be so intense that the higher and even the lower forms 

 of life such as we are now acquainted with will cease to be, and wiien all 

 inorganic life will have reached its greatest density. And between tliese 

 two great time-periods, the incoming and outgoing of organic life on the 

 earth, there will be a middle period of maximum variation and develop- 

 ment, in which the seasonal contrasts will present their widest variety, 

 and the organic world its greatest differentiation and growth. On the 

 other hand, the nearer we approach the two great time-periods, the 

 seasonal contrasts will be smaller, and the organic and inorganic differen- 

 tiations will bo fewer. And these conditions as to climate, life, and dif- 

 ferentiation are what we should expect in dealing with a cooling earth. 

 At one period in the history of the earth the heat which was given off was 

 such that the climatic conditions of the North and South Polar Zones as 

 to moisture and temperature were better suited to organic life than were 

 the other zones. A cooling earth, assuming the rocks to be generally 

 similar in the different zones, would sooner become suited for the abode of 

 life in the Polar Zones than elsewhere. More heat was given off from the 

 regions around the poles than from the region around the equator, for the 

 reason that a six-months day, followed by a six-months night, in the 

 Polar Zones, will produce wider variations of temperature than a twelve- 



