12G 



of an arch, every alternate couple only being connected together; the 

 intermediate two timbers being unconnected, and resting upon, in- 

 stead of supporting, the outer planking. The mode of joining the 

 different pieces of the same rib is also highly objectionable. It is 

 effected by the introduction of a wedge-piece, by which the grain of 

 the rib pieces is much cut, and the general fabric weakened, with a 

 great consumption of materials. The object of the introduction of 

 these wedge pieces or chocks, is to procure the curvature requisite in 

 forming a ship, when crooked timber is scarce ; but the curve may 

 be equally obtained by a different arrangement of materials, and with 

 less consumption of useful timber. 



After pointing out several other defects and disadvantages arising 

 out of the present mode of building mercantile ships, Sir Robert 

 proceeds to consider the best means of obviating them. He employs 

 shorter lengths of timber and of less curvature, consequently less 

 grain-cut, and their ends are connected by coaks or dowels, instead 

 of wedge pieces. In the event of a ship grounding, such a con- 

 struction is much better adapted to give support and strength to the 

 fabric than the former. 



The advantages of this new principle in practice appear from a 

 report of the officers of Woolwich Yard to the Navy Board, relating 

 to a comparison of the Talavera, built upon the improved construc- 

 tion, with the Black Prince, constructed in the usual "way. Another 

 important circumstance relating to the Talavera is, that her frame 

 consists of small timber, hitherto considered as only applicable to 

 frigates, but which, when properly combined, may, in Sir Robert's 

 opinion, be rendered equal in strength and economy to the large and 

 often grain-cut materials used in the frames of large ships. 



Several drawings accompany this paper, the inspection of which is 

 requisite to render the further details which it contains intelligible. 



On the Milk Tusks, and Organ of Hearing of the Dugong. By Sir 

 Everard Home, Bart. V.P.R.S. Read April 13, 1820. [Phil. 

 Trans. 1820, p. 144.] 



The skull upon which the following observations were made, was 

 sent to the author from Sumatra by Sir Thomas Stamford Raffles, 

 and is the only perfect specimen in Europe. The milk tusks were 

 first examined; and as their points only were visible, one of the bony 

 canals in which the tusk is contained was laid open : it was removed 

 from its socket, and cut through longitudinally, when it appeared 

 similar to the milk tusks of the narwhale and elephant, and like them 

 deficient in external smoothness as compared with the permanent 

 tusks. 



The milk tusk of the dugong is peculiar in having a shallow cup 

 attached to its base, apparently for the purpose of receiving the 

 point of the permanent tusk as soon as formed ; and as the milk tusk 

 advances in the act of being shed, the other may be directed for- 

 wards in the same course, which differs from that in which it set out. 



