340 K. Honda and S. Shimizu on Change of Length of 



rotating cylinder, the ends of which terminate in cones and 

 fit in the agate cups fixed on the heads of screws in the 

 brass socket BB. K is a collimator, L a lens, and E a 

 micrometer with ocular scale. The slit of the collimator is 

 illuminated by a gas-flame ; the light leaves the collimator 

 adjusted for a parallel beam, and is reflected by the mirror 

 M, and converges in the micrometer field through the lens L. 

 In the middle of the slit a very fine glass fibre is stretched 

 parallel to the edge, the image of which is clearly seen in 

 the micrometer. The vertical wire touches the rotating 

 cylinder under a suitable pressure ; if the wire elongates or 

 contracts the mirror rotates through a small angle, and the 

 corresponding displacement of the image of the fibre is 

 observed in the micrometer field. 



The magnetizing coil is 30 cm. long and gives a field of 

 37'97 c.G.s. units at the centre by passing a current of one 

 ampere. The wire to be tested is soldered into well annealed 

 soft copper wires of about the same diameter, as shown in 

 fig. 2. It is hung vertically in the axial line of the mag- 

 netizing coil so as to lie in a nearly uniform field. The pan 

 Fig. 2. 



Cct 



Te 



Fisr. 8. 



Cu 



a 



attached to the lower end of the wire carries in its under 

 face a few pieces of cotton which softly touch a wooden 

 stand for the purpose of damping, without producing sensible 

 pressure. The forms of the rotating cylinder and the brass 

 socket are drawn in fig. 3. 



The stand on which the brass socket is fixed can be made 

 to move up and dowm as well as forward and backward by 

 means of screws. By this arrangement the cylinder can be 



