286 Prof. A. Gray and Mr. A. Wood. Effect of a [Mar. 12, 



plane mirror is set at right angles to the optic axis in the principal 

 focus of a cylindrical lens. Between the lens and the eye a plate of 

 unsilvered glass is placed at such an angle as to reflect the rays from 

 some distant object through the lens on to the mirror, whence they 

 are reflected once more through the lens into the eye. The unsilvered 

 reflection is not necessary if the eye is held at some considerable 

 distance from the lens. In such an arrangement the image is not 

 enantiomorphic, the effect of the cylindrical lens-system being 

 neutralised by that of the mirror, but the image rotates when the lens 

 is rotated exactly as in an ordinary cylindrical telescope, and the plane 

 of polarisation is not affected by the rotation. 



" On the Effect of a Magnetic Field on the Eate of Subsidence of 

 Torsional Oscillations in Wires of Nickel and Iron, and the 

 Changes Produced by Drawing and Annealing." By Professor 

 Andrew Gray, F.B.S., and Alexander Wood, B.Sc. Beceived 

 March 12— Bead March 17, 1904. 



On May 15th, 1902, we communicated to the Boyal Society a paper 

 entitled " On the Effect of a Longitudinal Magnetic Field on the 

 Internal Viscosity of Nickel and Iron, as shown by Change of the Bate 

 of Subsidence of Torsional Oscillations." We described in that paper 

 the results of experiments on the rates of subsidence of torsional oscil- 

 lations in nickel and iron wires in fields of different strengths, and 

 showed that the effect of the field, or, more properly, of the magnetisa- 

 tion of the wire, is to increase the rate of subsidence in nickel and to 

 diminish it in iron. In nickel, it was pointed out, this effect rose to a 

 maximum at a certain field, from 100 — 180 C.G.S., according to the 

 initial amplitude, and thereafter diminished as the field was increased ; 

 while in iron the effect was in the main all produced at a field of 

 about 160 C.G.S. or rather less, and increased only slightly with 

 further increase of field intensity. 



The experiments described in the present paper are referred to 

 at the end of the former one as in progress, and some account of their 

 results is given ; and we propose now to describe them a little more in 

 detail. 



Experiments on the Effect of Drawing Down and of Annealing a Nickel 

 Wire. — A piece of the nickel wire formerly experimented on was 

 tested for subsidence in the manner already described, and then drawn 

 down, by being passed through a draw plate, from the diameter 

 1-4 mm. to 0*775 mm. The results are illustrated by fig. 1. Take first 

 curve I of that figure. It has for ordinates the differences between 



