558 Professor Dewar [Jan. 22, 



increased ninefold. The observations, so far as they go, accord with 

 this theory. In order to examine the effect of temperature, the ab- 

 sorption of a thickness of 3 cm. of liquid oxygen boiling under 1 cm. 

 pressure, or at a temperature of —210°, was compared with a like 

 thickness of the liquid boiling at atmospheric pressure. With the 

 colder liquid the bands in the orange and yellow were sensibly 

 widened, mainly on the more refrangible side ; the faint band in the 

 green was plainly darker, and the band in the blue appeared some- 

 what stronger. The difference between the temperatures of the two 

 liquids was about 27°, or approaching to one-third the absolute 

 boiling-point of oxygen. The density of oxygen at — 210° C. is not 

 known, but in any case it is greater than that at — 183° C, and an 

 increased absorption of about one-fourth by the cooling might be 

 anticipated. 



At the low temperature reached by the use of a hydrogen jet taken 

 in liquid air, the latter solidifies into a hard white solid resembling 

 avalanche snow. The solid has a pale bluish colour, showing by 

 reflection all the absorption bands of the liquid. 



The refractive power of the liquid, as determined by Prof. Liveing 

 and the author, was given in a previous lecture.* Later investigations 

 resulted in the determination of the dispersive power. The refractive 

 constant of the liquid oxygen was found to be almost identical with 

 Mascart's value for the gas, and similarly the dispersive constant in 

 the liquid and gas seems to be identical. 



Magnetic Properties of Liquid Oxygen. 



The remarkable magnetic properties of liquid oxygen were de- 

 scribed to the Royal Institution in a lecture delivered in 1892.t 

 Professor Fleming and myself have for some time past directed our 

 attention to the question of determining the numerical values of the 

 magnetic permeability and magnetic susceptibility of liquid oxygen,J 

 with the object of determining not only the magnitude of these 

 physical constants, but also whether they vary with the magnetic 

 force under which they are determined. 



Although a large number of determinations have been made by 

 many observers of the magnetic susceptibility of different liquids 

 taken at various temperatures, difficulties of a particular kind occur 

 in dealing with liquid oxygen. One method adopted for determining 

 the magnetic susceptibility of a liquid is to observe the increase of 

 mutual induction of two conducting circuits suitably placed, first in 

 air, and then when the air is replaced by the liquid in question, the 



♦ "Liquid Atmospheric Air," Proc. Eoy. Inst. 1893. 



t See Roy. Inst. Proc. June 15th, 1892, "On the Magnetic Properties of 

 Liquid Oxygen." Friday evening discourse, bv Professor J. Dewar, F.R.S. 



X Proc. Roy. Soe. vol. Ix. 1896, p. 283, " On the Magnetic Permeability of 

 Liqaid Oxygen and Liquid Air," by Professor J. A. Fleming, F.R.S. and 

 Professor J. Dewar, F.R.S. 



