404 Scientific Uses of Liquid Air. [Jan. 19, 1894. 



condition. In experiment (3) the first cooling shows a loss of 

 24 per cent., while in experiment (4) the first cooling shows a gain 

 of 12^ per cent. 



It is clear, therefore, that according to these experiments, every 

 magnet has individual characteristics that may either result in no 

 change on cooling or the addition or subtraction of from 12 to 24 

 j)er cent, in the magnetic strength. All the experiments, however, 

 show that a repetition of the cycle of heating and cooling brings the 

 magnet to a steady state, in which cooling always causes increase in 

 the magnetic strength of from 30 to 50 per cent., and the re-heating 

 brings about no loss in the original magnetic moment. Such a 

 marked alteration of magnetic strength might be used as a ther- 

 mometer in low temperature research, and it is my intention to 

 extend the inquiry to the lowest temperature that can be reached by 

 the evaporation of nitrogen in vacua, A simple mode of showing 

 the sudden alteration of magnetic strength on cooling, is to surround 

 a permanent magnet made up of a bundle of steel wires with a coil of 

 copper wire, leaving the ends of the magnet to project so that they 

 can be dipped in liquid air. When the copper wires are attached to 

 a galvanometer, and one of the ends of the magnet cooled, an induced 

 electrical current occurs, due to the sudden magnetic change. 

 Accurate observations must be made on the permeability and sus- 

 ceptibility of the magnetic metals at the temperature of boiling 

 liquid air, and the above results are an indirect guarantee that this 

 field of investigation will be fruitful in new scientific facts. 



This lecture has already covered a very wide field. It is easy 

 to put into a Friday evening discourse the work of a year. Members 

 and friends have chiefly contributed to the Research Fund, which 

 has enabled the Institution to extend the experimental plant needed 

 for the prosecution of research in this field of inquiry, and they 

 have strong claims to learn, in the first instance, the results of the 

 general laboratory work. My object has been to illustrate the 

 scientific uses of liquid air. To do this with any satisfaction requires 

 what may be called a good deal of scientific prospecting. It is one 

 thing to discover where the ore lies, it is another thing to produce 

 the refined metal. Investigations on the properties of matter at the 

 temperature of boiling liquid air, must be in the first instance rather 

 qualitative than rigidly quantitative. In my opinion scientific pro- 

 gress is best served by conducting the inquiry on these lines. It 

 will be easy to refine later on. 



I have to acknowledge the great assistance I have received in 

 the conduct of these experiments, from my excellent chief assistant 

 Mr. Robert Lennox, and I must also express commendation of the 

 way Mr. Heath has helped in the work. 



[J. D.] 



