TRANSACTIONS OF THE SECTIONS. 



253 



reading of weight No. 1. In tlie diagram the vertical scales being— for speed 12 knots 

 per inch, for inclination in 125 inches and vertical motion of vessel 12 inches per 

 inch, for motion of weights 24 inches per inch. 



The diagram shows that the vessel sank more deeply as the speed increased to 

 about 12 knots, when almost suddenly, with increasing speed, the boat rises ; and 

 this contiuues up to the highest speed attained, the depression at 12 knots being 

 about 5 inches, and the elevation at 19 knots 3 inches. Thus the greatest change 

 of level observed was about 8 inches. 



On a Machine for the Calculation of Tides. By Sir W. Thomson, F.K.S. 



On Methods of giving Distinctive Characters to Lighthouses. 

 By Sir W. Thomson, F.R.S., and J. Hopkinsox, B.Sc. 



On the Channel Tunnel*. By W. Toplet, F.G.S., Assoc.Inst.C.E. 



The author first described the geological structure of the shores of tlie Straits of 

 Dover, noting especially tlie water-bearing qualities of the various strata. The 

 most important bed in relation to this question is the ChaUc; the upper part of it 

 contains layers of ilints, which are wanting in the lower part. Water passes only 

 slowly through the mass of the chalk, but more freely along joints and fissures or 

 along the lines of flint. Below the Chalk come Gault, Lower Greensand, Weald 

 Clay, and Hastings Beds. Of these the Gault and the Weald Clay may be taken 

 as impervious beds. The author then passed on to note the lower beds, which come 

 to the surface near Boulogne, but wliicli are only known in the S.E. of England 

 by the Sub-Wealden boring. The various folds into which the strata have been 

 thrown were then noticed, and the relation of these to the structure of the district 

 was discussed. 



The author then referred to the various schemes which had been proposed fur 

 traversing the bed of the Channel, dwelling in greatest detail upon that of Sir J. 

 IIawk.shaw — a tunnel through the Challc, He alluded to the views of Prof. 

 Herbert as to the supposed existence of a large transverse fold iu the Channel, whicli 

 it was suggested might seriously interfere with the work, by bringing up beds 

 lower than the Chalk along the proposed line of tunnel. He was not prepared to 

 follow Prof. IJebert in his argument, believing that there was no evidence of such 

 difficulties as were suggested. It is frequently supposed that faults in the strata 

 would cause great inconvenience ; but the author showed, by reference to actual 

 workings in coal and other mines, that the danger here was exceedingly small, and 

 that there is no reasonable expectation of meeting with a larger quantity of water 

 tlian can be dealt with by pumping. 



The author referred to a proposal, by Prof. Prestwich, to construct a tunnel 

 through the Paljeozoic rocks; and al.so to one, first suggested by Mr. H. Willett, 

 for using in this way the Kimmeridge Clay, which occurs in great thickness in 

 the Sub-Wealden boring, and also exists on the French coast. He showed that a 

 tunnel through the Kimmeridge Clny would be quite feasible, the chief objection 

 being its length. He gave a preference to Sir J. Hawkshaw's scheme — a tunnel 

 through the Lower Chalk, and had little doubt that this could be successt'iilly 

 carried out. 



On a Machine for obtaining Motire Power from the Motion of a Ship among 

 Wave^. By Beauchamp Tower. 



This machine consists in principle of a weight supported on a spring, .so tliat it 

 can oscillate on the spring through a considerable range in a vertical line. Tlio 



* This subject lias been discussed in greater detail by the author in ' Quart. Journ, 

 of Science ' for April 1872. and ' Pop. Sci. Review ' for October J874. 



1875. ■ 19 



