248 



Experiments on Torsion and Flexure. [Jan. 30. 



light which will be afforded by another specimen to the indulgence of any 

 speculation regarding this bone ; in the meanwhile, I by no means wish to 

 deny that appearances are strongly in favour of the interpretation which 

 has been put upon it. 



In conclusion, I may remark that I am unaware of the existence of any 

 " law of correlation " which will enable us to infer that the mouth of this 

 animal was devoid of lips, and was a toothless beak. The soft tortoises 

 {Trionyx) have fleshy lips as well as horny beaks ; the Chelonia in 

 general have horny beaks, though they possess no feathers to preen ; and 

 Rhamphorhynchus combined both beak and teeth, though it was equally 

 devoid of feathers. If, when the head of Archceopterycc is discovered, its 

 jaws contain teeth, it will not the more, to my mind, cease to be a bird, than 

 turtles cease to be reptiles because they have beaks. 



All birds have a tarso-metatarsus, a pelvis, and feathers, such, in principle, 

 as those possessed by Arch(£opteryx. No known reptile, recent or fossil, 

 combines these three characters, or presents feathers, or possesses a com- 

 pletely ornithic tarsometatarsus, or pelvis. Compsognathus comes nearest in 

 the tarsal region, Megalosaurus and Iguanodon in the pelvis. But, so far 

 as the specimen enables me to judge, I am disposed to think that, in many 

 respects, Archceopteryx is more remote from the boundary-line between 

 birds and reptiles than some living EatittB are. 



II. " AccouDt of Experiments on Torsion and Flexure for the Determi- 

 nation of Rigidities.''^ By Joseph D. Everett, D.C.L., Professor 

 of Natural Philosophy in Queen's College, Belfast. Communicated 

 by Sir William Thomson. Received January 13, 1868. 

 (Abstract.) 



This paper describes a continuation of experiments related in two 

 former papers, read February 22, 1866, and February 7, 1867, — the sub- 

 stances operated on in the new series being wrought iron, cast iron, and 

 copper, and the mode of procedure being the same as in the latter of the 

 two preceding series. The results obtained, along with those published in 

 the former papers, are given below, the figures I., II., III. indicating the 

 paper in which the results are deduced. The values of M, n, and Jc are in 

 milHons of grammes weight per square centimetre. 





M, 

 Young's 

 modulus. 



n, 



Eigidity. 



k, 



Resistance to 

 compression. 



Poisson's 

 ratio. 



Specific 

 gravity. 



Glass, flint, I. 



614-3 



244-2 



423-0 



•258 



2-942 



Do. II. ... 



585-1 



239-0 



353-3 



•229 



2-935 



Brass, drawn, II.... 



1094-8 



372-9 



5701 (?) 



•469 



8-471 



Steel, cast, II 



2179-3 



834-1 



1875-6 



•310 



7-849 



Iron, wrought. III. 



1999-4 



783-8 



1484-1 



•275 



7-677 



Iron, cast, III 



1374-1 



542-3 



982-2 



•267 



7-235 



Copper, drawn. III. 



1255 8 



455-6 



1716-4 



•378 



8-843 



