148 REPORT — 1866. 



I decline to attempt to fix the mimber of new species, or even genera, which, 

 we are able to add to the list in the Survey Memoir ; for not only is the deter- 

 mination of fossil leaves at all times very unsatisfactory, but that list was not 

 intended for a monograph, and has neither drawings (except a few) nor the 

 exactness of description requisite for identification. Then, too, the nomen- 

 clature of fossil leaves is very unsettled, the same leaf having often half a 

 dozen different names. 



With regard to the species of fossil leaves, I believe the word " form " 

 might often with advantage be used where "species" is now universally 

 employed. "Species" is applicable only to the entire plant; "form" is 

 applicable to individual leaves. When we consider the variation often met 

 with in leaves growing on the same tree, I think we see reason for great 

 caution in determining what " forms " represent the existence of distinct 

 " species." 



[Mr. Mitchell exhibited photographs and drawings of some of the larger 

 and more interesting leaves]. 



Report of the Committee appointed to make Experiments on the differ', 

 ence between the Resistance of Water to Floating and to Immersed 

 Bodies. The Committee consists of John Scott Russell, C.E., 

 F.R.S. ; James H. Napier; Professor Rankine, C.E., F.R.S.; 

 and W. Froude. 



The following Heport describes the experiments made by the Committee. 



The Committee held sevei'al meetings in the course of the winter and 

 spring of 1864-65, and agreed to a programme of experiments, of which the 

 following is a summary : — 



" 1 . Two models to be made of painted wood, designated respectively as 

 A and B. 



" 2. The models to be ship-shape, and each of them to consist of two equal 

 and similar halves joined together at the middle water-line. 



Elements of Models. 



A. B. 



Length 4 feet 4 feet 



Breadth, J- of length 0-571 foot 0-571 foot 



Total depth 0-571 foot 0-364 foot 



Form of midship section Circle Elhpse 



Area of midship section 0-256 sq. foot 0-163 sq. foot 



Eatio of those areas 1 : 0-6366 



Form of water-lines of fore body Harmonic curves 



Form of water-lines of after body Trochoids 



(Stem and stern-post at first intended to 



be vertical straight lines, but afterwards 



rounded off to prevent the corners from 



being chipped.) 

 Length of fore body : length of after body : : 3 : 2 3:2 



Mean girth 1-45 feet 1 foot 



Displacement when half immersed 17-228 lb. 10-986 lb. 



