Hill. — Prohle^ns of Arctic Exploration. 389 



surface-waters within the warm and cold oceans respectively 

 has a range of 50°, whilst the range of temperature between 

 the waters at great depths in the same oceafis is not more 

 than 5°. It is curious and important to notice how the 

 surface- and depth-temperatures of the waters tend to ap- 

 proximate each other in proceeding from the equator to the 

 poles. The surface-temperature at the equator is 80°, and 

 within the arctic circle 32° or lower, whilst at 800 fathoms the 

 temperature falls to 35° at the equator, and to 30° or more 

 within the circumpolar area. 



It follows from these facts — first, that surface-movements 

 of the waters of the ocean are greater than depth-movements ; 

 and, second, that depth-movements in the warmer oceans are 

 much more pronounced than within the cold oceans. These 

 laws have an important bearing upon the past and present 

 condition of the earth's surface, as it must be evident that 

 these conditions have not always existed. 



I have purposely dwelt on this interesting topic at some 

 length, as it is highly suggestive in connection with the 

 nebular theory of the earth, as it is also in the matter of 

 aerial movements. No one who considers the nebular 

 theory as bearing on the life-history of the earth but must 

 be struck with the harmony of the records that have 

 come to us through the brave men who have striven to 

 solve the mystery of the north pole. Those records imply 

 a .great past in the life-history of the now frigid zone, but 

 they also imply a growth, a development, and a descension. 

 The time was when the life-possibilities in those inhospitable 

 regions were greater than they are now, and the question 

 must be asked how the changes in activities have been 

 brought about. I think it may be assumed that the depth- 

 movements of the ocean were much more pronounced in 

 former times than they are at present, for the waters were 

 then heated more by convection than by conduction. When 

 the earth was many degrees warmer than now the surface- 

 contrasts were not so wide, and, as a consequence, surface- 

 movements, like currents which are produced by heat, were 

 not so pronounced. 



Let me illustrate what I wish to convey by means of two 

 simple experiments. First, take a bottle — an ordinary water- 

 bottle will do — and fill it about one-third full with water at a 

 temperature of 60°, the water being slightly coloured wath a 

 blue tint. Let this be followed by a similar quantity of water 

 tinted red at a temperature of 100°, and then fill up with 

 boiling water having a green tint. In the second experiment 

 reverse the order of filling the bottle by putting in the boiling 

 water first, and then observe the results in each case. In the 

 first illustration the movements of the water will be com- 



