578 PLUCKER ON THE ACTION OF THE MAGl/ET, ETC. 



the existence of an analogy between heat and the power of 

 the magnet : both expand air and gaseous bodies. It has been 

 shown, that around a magnet, even the air which is not enclosed 

 becomes rarefied by it; and this rarefaction must necessarily 

 increase with the approximation of the poles. Hence Mariotte's 

 law, strictly considered, ceases to be correct as ordinarily admit- 

 ted. The barometer or manometer does not indicate the density 

 of the air, when w^e take into consideration the temperature 

 only without regard to its diamagnetic condition. 

 Bonn, 22nd and 31st of January, 1848. 



/ hoJBaq 



