462 Geological Society : — 



reduction. These results relate to the disturbances of level which 

 accompany the disturbances of motion when the liquid has a free 

 upper surface, to the waves which originate in those disturbances of 

 level, and the action of those waves in dispersing energy and so 

 causing resistance to the motion of the vessel, to friction, or skin- 

 resistance, and the " wake" or following current which that kind of 

 resistance causes the disturbing solid body to drag behind it, and to 

 the action of propelling instruments in overcoming different kinds of 

 resistance. 



The resistance caused by viscosity is not treated of, because its 

 laws have been completely investigated by Mr. Stokes, and because 

 for bodies of the size of ships, and moving at their ordinary velo- 

 cities, that kind of resistance is inconsiderable compared with skin- 

 resistance and wave-resistance. The resistance caused by discon- 

 tinuity of figure is stated to be analogous in its effects to friction ; 

 but it is not investigated in detail, because ships ought not to be 

 built of discontinuous (commonly called " unfair") figures. 



Supplement. 



The author in the first place calls attention to the agreement be- 

 tween the position of the points at which there is no disturbance of 

 the pressure on the surface of a sphere, as deduced from Dr. Hoppe's 

 investigation, published in 1856 (Quarterly Journal of Mathematics), 

 and on the surface of a short vertical cylinder with a flat bottom, as 

 determined by the experiments of the Rev. E. L. Berthon before 

 1850 (Proc. Roy. Soc. vol. v. 1850 ; also Transactions of the So- 

 ciety of Engineers, 6th of December, 1869). The theoretical value 

 of the angular distance of those points from the foremost pole of the 

 sphere is sin -1 f =41° 49'; the value deduced from experiment is 

 41° 30'. 



The author then adds some remarks on a suggestion made by Mr. 

 William Froude, that the wave-resistance of a ship is diminished 

 when two series of waves originating at different points of her sur- 

 face partially neutralize each other by interference ; and states that, 

 with regard to this and many other questions of the resistance of 

 vessels, a great advancement of knowledge is to be expected from the 

 publication in detail of the results of experiments on which Mr. 

 Froude has long been engaged. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 392.] 



November 10th, 1869.— Prof. T. H. Huxley, LL.D., F.R.S., 



President, in the Chair. 



The following communications were read : — 



1. " Australian Mesozoic Greology and Palaeontology." By Charles 

 Moore, Esq., F.G.S. 



The author referred to the observations of Professor M'Coy and 

 the Rev. W. B. Clark on the occurrence of fossils of Mesozoic age 



