On Secular Local Changes in the Sea-level. 201 



volumes of saturated vapours at given boiling-points, and the 

 calculated volumes which they would fill if they were perfectly 

 gaseous — and also between the actual latent heat of evaporation 

 and the calculated latent heat of perfect gasefication. The general 

 results are in accordance with what is already known, viz. that 

 the actual volumes of vapours are less than those corresponding 

 to the perfectly gaseous state, and the actual latent heat of eva- 

 poration less than the latent heat of gasefication ; and the author 

 further points out that the differences, in the case of steam, in- 

 crease nearly as the absolute temperature. 



XXXI. On Secular Local Changes in the Sea-level. 

 By D. D. Heath, M.A., F.G.S.* 



EMINENT geologists incline to the belief that at the "glacial 

 epoch " a huge and more or less continuous capping of ice 

 covered the whole arctic and subarctic region. And it is con- 

 ceived that such a phenomenon may occur whenever, during a 

 period of extreme excentricity of our orbit, the northern winter 

 is nearly coincident with the time when the earth is in aphelion. 

 In such a case, it is argued, we shall have an extreme climate, 

 with severe and somewhat protracted winters and hot but short- 

 ened summers in the north, and a very equable climate in the 

 south ; and this will produce an accumulation of permanent ice 

 in the one region and its disappearance in the other. 



And these considerations have suggested to Mr. Croll in Eng- 

 land, as well as to M. Adhemar in France, the thought that this 

 gathering up of solid matter at one extremity of the earth would 

 heap up the waters also of the ocean in high northern latitudes, 

 and so account for the fact that over large areas in those latitudes 

 the sea has left its mark on mountain-sides 1000, 2000, or more 

 feet higher than its present relative level. 



The general theory of changes of sea-level involved in this sug- 

 gestion appeared to me well worth mathematical treatment, pur- 

 sued to some rough numerical results — not only on account of 

 the special facts of the glacial epoch, but because similar effects 

 must follow upon any great change in the position of the solid 

 " parts of the earth, such as the rising of a continent. I should 

 therefore have thought the following investigation worth com- 

 pleting and publishing, even though I had taken Mr. CrolPs 

 letter to the ' Reader ' of the 13th of January last, wherein he 

 renounces the opinion that the theory will sufficiently account 

 for the special facts, to be conclusive on that point. 



But the truth is (as was pointed out by Mr. Fisher in the 



* Communicated by the Author. 



