1864.] On the Excavation of the Valley of the Somme, 135 



find matter for industry and patience. I have done a little in this subject, 

 but not enough to deserve any special mention. In order, however, to 

 diminish the difficulties, the investigation may be provisionally restricted t® 

 the mutual actions of the envelopes, neglecting for the time that of the 

 nuclei, which may be considered as a disturbing cause, for which some 

 correction may afterwards have to be made. 



So much then for the mathematical and theoretic development of mole- 

 cular mechanics. There remains the third part, which, though the most 

 laborious of all, will yet give the greatest pleasure to scientific men ; since 

 it is less dry, and opens a way for attaining the end aimed at in the natural 

 sciences. Of this third part I will add a few words. 



III. Application of the Principles of Molecular Mechanics. 



[Under this head the author points out the various properties of bodies 

 which would have to be explained, and of which he conceives an explana- 

 tion might be afforded could the mathematical calculations be effected 

 which are required for the elaboration of his theory, and enunciates the 

 following conclusions as deduced from his explanation of the impact of 

 bodies.] 



1 . If a body does not contain any repulsive elements, it cannot cause any 

 retardation in the movement of any impinging body. 



2. Again, if the medium through which a body moves contain no repul- 

 sive elements, no retardation of its motion can take place. 



3. If a medium does contain repulsive elements, retardation must neces- 

 sarily take place. 



4. Consequently, as the planets in their movements through the sether 

 do not suffer any loss of velocity, it must be concluded that the sether does 

 not contain any repulsive elements at all, and that its elasticity must be 

 explained without any recourse to repulsive forces. 



This last inference is somewhat wonderful, and decidedly curious : but- 

 after much consideration it appeared to me so natural, and so well harmo- 

 nizing with other truths and scientific theories, that I ceased to hesitate 

 about its adoption and gave it a most decided assent ; whether wisely or 

 not, I leave others to judge. 



III. " On some further Evidence bearing on the Excavation of the 

 Valley of the Somme by River-action, as exhibited in a Section 

 at Drucat near Abbeville.^' By Joseph Prestwich, E.E.S. 

 Received January 29, 1864. 



On the occasion of a late visit to Abbeville, I noticed a fact which appears 

 of sufiicient interest, as bearing upon and confirming one of the points 

 treated of in my last paper, to induce me to submit a short notice of it to the 

 Royal Society. It occurs in a tributary valley to that of the Somme, but 

 necessarily forms part of the general phenomena affecting the whole basin. 



