116 Mr. J. Hunter on the Absorption 



rents, the anomalous magnetizing was not to be produced to the 

 same extent as when the unmagnetic state had come of itself in 

 the manner just described. 



It follows from this that the apparently unmagnetic state 

 which is brought about by contrary magnetizing, and which 

 Marianini* has named "latent " or " dissimulated " magnetism, 

 is also in these experiments nowise equivalent to the originally 

 unmagnetic condition. 



The same irregularities were displayed by an iron bar of 103 

 millims. in length and 20 millims. diameter, and which was 

 magnetized in the same spiral up to about 45. The numerical 

 values of the residual magnetism for this bar were not very con- 

 siderably different from those which the thicker bar had showed 

 at the same intensity of current. 



For the rest, both bars were of the softest iron which I was 

 able to get. In conclusion, I have still to remark that in these 

 experiments the magnetizing was effected, as a rule, by means 

 of a gradually increasing stream, and that, every time, the iron 

 core was exposed to the magnetizing influence for several 

 seconds. I have thus taken into account the circumstance first 

 shown by Faraday -f, that for the complete development of elec- 

 tromagnetism a measurable time is required {. 



The striking numerical difference in the residual magnetism 

 after sudden and after gradual stoppage of the current is in every 

 instance easy to show ; on the other hand, the observation of 

 anomalous magnetism requires undoubtedly delicate experi- 

 ments ; it is also obvious that the appearance of the latter must 

 depend upon the nature of the kind of iron, and so far must be 

 more or less accidental. 



Innsbruck, November 2, 1863. 



XX. On the Absorption of Gases by Charcoal. 

 By John Hunter, M.A.§ 



IN a previous communication I have noticed briefly the results 

 of some preliminary observations on the absorption of gases 

 by different varieties of charcoal. These experiments have been 

 continued, and the present paper contains some additional facts 

 connected with this subject. The same method was adopted as 

 before : the gases, carefully dried, were collected over mercury, 



* Berliner Bericht (Fortschritte der PhysiJc), 1847, p. 488. 

 t 19, 22, and 23, 'Experimental Researches.' 



X In Faraday's experiments this time amounted to from some seconds 

 up to perceptibly over a minute, according to circumstances. 

 § Communicated by the Author, 



