238 LIGHT SCIENCE FOR LEISURE HOURS. 



spirit lamp placed beneath it ; thus representing the 

 relative thermal conditions of the polar and equatorial 

 basins. A colouring liquid viscid enough to hold 

 together in the water, while mixing with it sufficiently 

 to move as its moves, being then introduced, the liquid 

 as it impinged on the ice was seen to sink rapidly to 

 the bottom, then, to flow slowly along the floor of the 

 trough towards the opposite extremity, then gradually 

 to rise beneath the heated plate, and then to flow slowly 

 along the surface towards the glacial end, repeating 

 the same movement until the ice had melted.' 



It will be observed that in this experiment the effect 

 of cold is not exerted alone, so that it by no means 

 proves that the arctic cold is the chief agent in pro- 

 ducing the system of oceanic circulation. Moreover, 

 the conditions of the polar and equatorial basins are in 

 one respect not accurately (or even nearly) reproduced, 

 for the real arctic area is very much smaller, compared 

 with the real equatorial area, than in the case of the 

 experiment. Indeed it appears to me that Dr. Carpenter 

 paid far too little attention to the relative smallness of 

 the arctic area. This may have been partly due to the 

 erroneous ideas suggested by the ordinary maps on 

 Mercator's Projection, in which, as I have already 

 mentioned, the arctic regions are enormously exagger- 

 ated. It is almost impossible to study such a map as 

 that which illustrates this paper (see page 217) without 

 feeling that the theory presented by Dr. Carpenter will 

 scarcely hold water, or rather if this way of presenting 

 the argument be permitted that the arctic area does 



