298 Proceedings of Philosophical Societies. [Aprii,, 



much short of the mean as the other exceeds it, they are ultimately- 

 separated twice the usual distance, or to 34'. The paper was 

 concluded with some further directions for cutting and arranging 

 tlie prisms for the above purpose. 



March 2. — A paper, by Sir R. Seppings, was begun, on anew 

 Principle of constructing Ships for the mercantile Navy. In 

 the present mode of constructing ships, only half the timbers are 

 united, so as to constitute any part of an arch, every alternate 

 couple only being connected together ; the intermediate two 

 timbers being connected with, and resting upon, instead of 

 supporting the outer planking. The mode of joining the diffe- 

 rent pieces of the same rib are also highly objectionable, this 

 being at present effected by the introduction of wedge pieces, 

 by which the grain of the rib piece is much cut, and the general 

 fabric weakened ; besides, there is a great consumption of 

 materials. The object of these wedge pieces, or choaks, is to 

 produce the necessary degree of curvature when crooked timber 

 is scarce ; but the author showed that this curvature might be 

 equally obtained by a different arrangement of materials, and 

 with less consumption of useful timber. After pointing out 

 several other defects and disadvantages attending the present 

 mode of constructing mercantile ships, the author considered the 

 best modes of obviating them. He recommended that shorter 

 lengths of timber and of less curvature (which will have the 

 advantage of being less grain cut), should be employed, and that 

 these pieces should be connected at their ends by coaks, or 

 dowells, instead of wedge pieces. 



The author then proceeded to point out the advantages of 

 these improvements, and mentioned a report on the subject by 

 the officers of Woolwich yard, respecting a ship which had been 

 constructed on the plan in question. One great advantage stated 

 to attend this plan was, that smaller timber may be employed 

 than usual in the construction of large ships, an object of the 

 first importance at present when large timber is become so 

 scarce. Drawings illustrative of the different points accompa- 

 nied the paper. 



March 9. — A paper was read, by J. A. Ransome, Esq. 

 on a Peculiarity iu tlie Structure of the Eye of the Batena 

 Mysticetus. On removing a portion of sclerotic coat of the eye 

 of this animal so as to expose one hemisphere of the choroid 

 coat, the author opened into a large sinus containing a blood- 

 vessel, v^'hich passed forward in the direction of the iris. On the 

 upper and lower surfaces of the sclerotica are two foramina for 

 the passage of vessels ; on its flat and posterior surface is a hole 

 for the transmission of the optic nerve ; and on each side corres- 

 ponding with the long diameter of the eye, are two other foramina 

 with large funnel-shaped mouths, which extend through the 

 substance of the coat, and terminate at its junction with the 

 cornea. These foramina were considered by Mr. Hunter as 



