1889.] 



Gas Flame. Magnetisation of Cobalt. 



41 



I should add that. Mr. Fowler has glimpsed a line less refrangible 

 than that at 500 in the spectrum of the ring nebula in Lyra. If 

 this should turn out to be the carbon fluting at 517, it would seem 

 that in that nebula we may have a state of condensation between 

 those represented by the nebulae of Orion and Andromeda, the 

 carbon replacing the A, 500 fluting of magnesium in the nebuhe, as 

 apparently happens in comets on their approach to perihelion. 



III. " Some Observations on the Amount of Luminous and Non- 

 luminous Radiation emitted by a Gas Flame." By Sir John 

 Conroy, Bart., M.A., Bedford Lecturer of Balliol College 

 and Millard Lecturer of Trinity College, Oxford. Com- 

 municated by A. G. Vernon Harcourt, LL.D., F.R.S. 

 Received November 11, 1889. 



[See page 55.] 



IV. " On the Effects of Pressure on the Magnetisation of 

 Cobalt." By C. Chree, M.A., Fellow of King's College, 

 Cambridge. Communicated by Prof. J. J. Thomson, F.R.S. 

 Received November 22, 1889. 



(Abstract.) 



It has long been known, from the classic researches of Dr. Joule, 

 that a rod of iron free from stress increases in length when magne- 

 tised in a comparatively weak field. When, however, the strength of 

 the field is continually raised, it has been found by Mr. Shelford 

 Bid well that the rod ceases to increase in length, and then shortens, 

 so that in a sufficiently strong field the length becomes less than it 

 was originally. It has also been found by Villari, Sir W. Thomson, 

 and others that when a rod of iron is exposed to successive loadings 

 and unloadings of a given weight in a magnetic field, there appears a 

 corresponding cyclic change of magnetisation. In this cyclic change 

 the maximum magnetisation occurs when the load is "on," or when 

 the load is " off," according as the field is weaker or stronger than a 

 certain critical field depending on the load, called by Sir W. Thomson 

 the Villari critical field. 



Cobalt has been found by Mr. Shelford Bidwell to shorten when 

 magnetised in weak fields, but to lengthen in very strong fields. The 

 field in which it ceases to shorten is very much higher than the field 

 in which iron ceases to lengthen. Also in weak fields Sir W. Thomson 

 has found the magnetisation of a cobalt rod under cyclic applications 

 of tension to be least when the tension is "on." 



