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SCIENCE PROGRESS 



manganese sulphate which may serve as an indication of the 

 general results found. 



TABLE VI 

 Susceptibility of Magnesium Sulphate. 



If the special deviation in the anhydrous salt at very low 

 temperatures is not considered, it appears that with A 1 = 24 the 

 anhydrous salt follows the relation expressed with fair approxi- 

 mation. If the number of magnetors is calculated for each 

 molecule they are each found to be 29. The same result is 

 found for crystallised and anhydrous ferrous sulphate, where the 

 number of magnetors is found to be again equal, but 26, putting 

 A 1 = 31. The deviations may be considered as due to the much 

 greater effect which the energy of the magnetors has in relation 

 to the heat energy at very low temperatures. 



By using the conceptions of zero point energy and of 

 Plank's radiation theory it is found that the zero point 

 energy = | hv (where hv = constant of Plank's radiation 

 formula, and v = frequency of the rotational movement of the 

 vibrator). The other Plank's constant k appears in the value 

 which is found to a first approximation for A 1 of Table VI. 



i.e. A 1 = -t—°. If this has a value of &6 for crystallised salt, and 



83 for the anhydrous, it is found that the observed and the 

 calculated values agree within the errors of experiment until 

 very low temperatures are reached as mentioned above. 

 The quantity v is inversely proportional to the moment of 

 inertia of the molecules. Hence where this is very large with 

 large molecules as with gadolinum sulphate Gd 2 (S0 4 ) 3 8H 2 the 

 deviations from Curie's law might be expected to be small, 

 which indeed is the case even to hydrogen temperature. 



