43^^ Ti':RKi:s'rKi.\i. piivsics. 



the air. This g-ives a point of contact with Alichelson's work 

 referred to hy Prof. Morrison, and offers an encouraging' field 

 tor South African investigation. 



The whole (|uestion of underground water is of special im- 

 portance. In Australia this has heen realized, where it has heen 

 the suhject of many reports, and is still under investigation. In 

 tracing the source of water, the temperature at emergence may 

 furnish a clue; and this leads to prohlems in the passage of 

 heat along these water chaimels. 



The determination of the heat conductivity of the various 

 rocks should be carried out systematically, and the temperature 

 gradient downwards found for different places. There are ob- 

 vious practical issues in connection with the cooling of deep- 

 level mines in addition to the scientific imi)ortance of ha\ing geo- 

 physical constants collated for dift'erent parts of the earth. 



Of rather a different kind is the problem of the motion of 

 sand on land. Practical engineers have dealt with this f|tiestion 

 from time to time, in order to ])revent the devastation of special 

 districts, lilsewhere observations have been made on the rate 

 and mode of travel af sand-dunes. On the rii)i>le formation in 

 sand a good deal of descriptive work has been done, and recently 

 the importance of the subject in connection with pakeontolo^y 

 has given a further stimulus in this direction.''' 



(Received Novcinber '^tli. i<;i7). 



Curvilinear Space.— Dr. de Sitter, of Groningen. in 

 a ])ai)er on " lunstein's Theory of ( iravitation," has drawn atten- 

 tion to some curious consequences of the assumption of cur\ ilinear 

 space. One of these is the theoretical existence of a point where 

 the ordinarx" conce})tion of three dimensions in space and one in 

 time is reduced to s|)ace only, with no time at all. This can only 

 refer to an epoch before the beginning or after the end of eternity. 

 Another — somewliat paradoxical — result, i^ that for a suitable 

 \alue of the curvature of s])ace. light from the l)ack of the sun 

 shotild be faintly visible at the opposite point of the sky. 



* E. M. Kindle: "Recent and Fossil Rijiple Marks." — Canada. Dcpt. of 

 Mine.s. Geological Survey, ]\Tuscuni I'ulktin. \o. 25. 



