Mechanical Science, 333 



head is north, and in the starboard section of the lower deck 

 when the vessel is moored with her head north-west. For the 

 proofs of this we refer to Mr. Harvey's paper on the Dlstribvtion 

 and Changes of the Magnetic Intensity in Ships of War, contained 

 in the second part of the Philosophical Transactions for 1824.. 



In a ship under the circumstances before mentioned, the inten- 

 sity of the larboard section will be found to increase 1-26 from 

 the upper to the lower deck, when the vessel's head is moored 

 due north, the magnetic intensity of the earth being represented 

 by 100; but a diminution of the attractive power in the same 

 section, amounting to 12*64, will be found to take place, when 

 the ship's head is directed to the east ; and an increase of 7*79 

 when the bow bears north-west. In the middle section of the 

 vessel, a minute decrease of 089 will be perceptible from the 

 upper to the lower deck in her first situation ; a rather greater 

 increase of r79 when her head is east, and a diminution of 2*43 

 when it is north-west. So also, in the starboard section, the 

 magnetic influence will be found to decrease from the upper to 

 the lower deck, when her head is north, by the small quantity 

 2*68 ; on the contrary, a rapid increase of 13-47 when it becomes 

 east ; and a considerable diminution, amounting to 10*32, when 

 her head bears north-west. — Ibid. 



In the middle and starboard sections of the poop ; in the three 

 sections of the forecastle ; in the starboard section of the upper 

 deck, and in the middle and larboard sections of the lower deck, 

 the stations at which the greatest and least intensities are respec- 

 tively found, when the bow of the vessel is due north, will be 

 found still to maintain the same property, when her head is 

 moored north-west ; — but, in the larboard section of the poop, 

 and the starboard section of the forecastle, the same principle 

 will be only found to hold good when the bow of the ship bears 

 due east. In the middle and larboard sections of the upper deck, 

 however, the points of maximum intensity will be found to pre- 

 serve their situations in the northern and western positions of the 

 ship ; but the points of minimum intensity will be observed to 

 approach the bow, in the latter situation. A similar property with 

 respect to the least intensities will also be found in the middle 

 and starboard sections of the lower deck, when the vessel is 

 moored with her head to the north and east. In these two last 

 positions of the vessel, the points of greatest and least intensity 

 will be found mutually to exchange places at some of the stations ; 

 the point of maximum intensity in the northern position of the 

 ship becoming in the eastern that of minimum intensity, and the 

 converse. These singular changes will be found in the middle 

 and starboard sections of the poop ; in the middle and larboard 

 sections of the forecastle, and the larboard section of the upper 

 deck. A point in the middle section of the lower deck, two- 



