On the Origin and Office of the Alburnum of Trees. 299 

 may be used where people are on shore, to assist when aline 

 is thrown. 



Fig. 5. Shows a grapnel which may also be fired from a 

 common cannon ; the collar slides along it in the same man- 

 ner as that in fig. 4, to allow the head of the pin to go clown 

 to the wadding within the cannon; ii, are two pins on 

 which the ring k, is moveable ; /, the block or pulley fast- 

 ened to the ring; m, the endless or double line running 

 through it. 



This method may be used with great advantage, where a 

 ship is stranded near the shore ; but where a mortar is on 

 board, the use of the shell and line is the most certain. 



Fig. 6. Shows the method of forming a raft, by lashing 

 together with ropes, five empty water-casks belonging to 

 the ship. 



Fig. 7- Represents the raft ready for "use ; the apparatus 

 n to hold the person upon it, is made from a seaman's chest 

 with holes cut in the sides of it, to allow the person within 

 it firmer hold, and to let out the water that may be thrown, 

 into it from the waves ; oo, are two pulleys attached to the 

 ends of the chest, and through which the line is to run; 

 the raft is to be ballasted underneath, to prevent it from up- 

 setting. 



The whole apparatus is so arranged as to be inclosed in 

 a small box, as may be seen by a reference to that in the 

 Society's possession. 



XLIV. On the Origin and Office of the Alburmim of Trees. 

 In a Letter from T. A. Knight, Esq.^ F.R.S., to Sir 

 Joseph Banks, Bart. K.B. P.R.S.* 



MY DEAR SIR, 



In my last communication I endeavoured to prove that the 

 bark of trees is not subsequently transmuted into alburnum ; 

 and if the statements that I have there given be correct, 

 they are, I conceive, decisive on the point for which I con- 

 tended: and if the bark be not converted into alburnum, 

 ihe experiments of Duhamel, and subsequent naturalists, 



* From Philosophical Transactions for 1308. Part II. 



and 



