138 



Dr. J. Hopkinson. 



[Jan. 23, 



The ten stars referred to are to be found within an area of less than 

 two square degrees of the sky, and in the table given are the co- 

 ordinates of their positions with reference to theta Orionis. The 

 measurements of the diameters of their photo-images on a scale of 

 0*00002 of an inch are also given. 



II. " Physical Properties of Nickel Steel." By J. Hopkinson, 

 D.Sc, F.R.S. Received January 16, 1890. 



Mr. Riley, of the Steel Company of Scotland, has kindly sent me 

 samples of wire drawn from the material concerning the magnetic 

 properties of which I recently made a communication to the Royal 

 Society. As already stated, this material contains 25 per cent, of 

 nickel and about 74 per cent, of iron, and over a range of temperature 

 from something below freezing to 580° C. it can exist in two states, 

 magnetic and non-magnetic. 



The wire as sent to me was magnetisable as tested by means of a 

 magnet in the Ordinary way. On heating it to a dull redness it 

 became non-magnetisable whether it was cooled slowly or exceedingly 

 rapidly by plunging it into water. A quantity of the wire was 

 brought into the non-magnetisable state by heating it, and allowing 

 it to cool. The electric resistance of a portion of this wire, about 

 5 metres in length, was ascertained in terms of the temperature ; it 

 was first of all tried at the ordinary temperature, and at temperatures 

 up to 340° C. The specific resistances at these temperatures are 

 indicated in the curve by the numbers 1, 2, 3. The wire was then 



cooled by means of solid carbonic acid, the supposed course of change 

 of resistance is indicated by the dotted Hue on the curve, the actual 

 observations of resistance, how r ever, are indicated by the crosses in 



