VARIATION OF THE COMPASS* 383 



//* Pieces of board with notches in them, fastened to the Machine for 



boxj to receive the bars. cutting the 



m. GroQve for the plough to work in. ^^ ' ' 



ft is evident from the positions of the press, that the 

 plough must be worked on an inclined plane; but this, 

 instead of an objection, is a considerable advantage, be- 

 cause the workman has much more power in that direc- 

 tion, than on a level. 



The press requiring to be turned round to cut the top 

 and bottom of the book, the plough must be worked 

 left as well as right handed, but this is acquired by a few 

 minutes practice. ' 



The same plough is used as with the common press. 



J. J. Hawkins. 



Dalbi/ Terrace^ City Roacl^ 

 May 29, 1805. 

 Charles Taylor, Esq. 



VII. 



Observations on the Permanency of the Variation of the 

 Compass at Jamaica. In a Letter from Mr. James 

 Robertson to the Right lion. Sir Joseph Banks, K.B, 

 P. R, S. (^-c*. 



Sir, 



.S any improvement, or discovery in the arts and sci- Generalintro- 

 ences, will, I am persuaded, experience your favourable 

 reception, I have the honour of submitting to your con- 

 sideration a discovery I have made on a subject, the state 

 of which can only be ascertained by observations made 

 from time to time, as it is not regulated by any known 

 law of Nature; I mean the variation of the magnetical 

 needle. 



This discovery may not only excite others to make, 

 and repeat, observations in different parts of the globe, 

 but, by causing this changeable quality to be better under- 

 stood, may contribute to the benefit of navigation, and 



♦ Phil. Trans. i8o6. 



F F f 2 commerce, 



