34 MAGNETISM, 



weighing more than a drachm, on being ignited, was completely dis- 

 solved in a jar of oxygen, without in the slightest degree destroy- 

 ing its transparency. The union of the two, formed carbonic 

 acid gas, which produced in lime water the same changes as 

 those induced by the expired air. 



OBSERVATIONS 



ON THE MAGNETISM TO WHICH THE IRON IN A SHIP IS LIABLE, 



BY INDUCTION, FROM TERRESTRIAL MAGNETISM; AND 



HOW FAR ITS INFLUENCE ON THE COMPASSES 



MAY BE CORRECTED BY PROFESSOR 



barlow's PLATE. 



The subject of this paper is an enquiry, whether Professor Bar- 

 low's plate for correcting the deviation of the compass-needle, on 

 ship-board, will actually do so under all circumstances : and, in 

 order to arrive at a conclusion, it is necessary to explain the 

 principles on which Mr. Barlow grounds his investigations. 



He supposes, that magnetic phenomena are due to the exist- 

 ence of two fluids, in a greater or less degree of combination, 

 (Page 151) and such that the particles of the same fluid repel, and 

 those of an opposite nature attract each other, and that these 

 fluids exist in iron in a state of combination, until their state is 

 disturbed by some exciting cause: that, in bodies already mag- 

 netical, these fluids are in a state of separation ; that, when a 

 piece of metal, containing the concentrated fluid, is brought near 

 to another piece containing the latent fluids, the concentrated 

 action of each fluid, in the magnetised body, will act on the 

 latent fluids, in the quiescent body, by repelling those of the 

 same, and attracting those of a contrary nature, and thus impress 

 a magnetic force or action, which will remain only while the two 

 bodies maintain their respective situations. (Page 152) 



The author concludes, that in all iron bodies or system of 

 bodies, a centre of attraction exists, from which he deduces all 

 the effects of local attraction in a ship, likely to affect the com- 

 passes and the guns, ballast, and metallic fastenings in a ship, 

 preserving their relative situations with respect to the steering 

 compasses ; he conceives that the Correcting Plate may be so 

 fixed, as to counteract all the effects of the iron on board. 



