2 MB. H. TOMLINSON ON THE INFLUENCE OF STRESS AND 



concentric brass tubes, 4 feet in length, and enclosing between them an annular space, 

 about a quarter of an inch thick, which could be filled with water. The wire hung 

 vertically in the axis of the' air-chamber, and at its lower extremity & was soldered 

 to a copper rod, b c, about '3 centim. in diameter, which was in turn connected to the 

 horizontal bar, V V. From V V were suspended two cylinders of equal mass and 

 dimensions, placed at equal distances from the axis of the wire. The nature of the 

 cylinders and their mode of suspension to the bar V V have been described in a 

 previous memoir on this subject.* The box B permits of free oscillation of V V and 

 its appendages, and is provided with air-tight fitting doors, whilst the glass window, 

 C, allows the vibrations of the wire to be measured by means of the usual mirror- 



lamp-and- scale arrangement, which is sufficiently shown in the figure. The base of 

 the air-chamber, A, is let into the top of a stout wooden table pierced with a circular 

 aperture, o, through the centre of which passes the rod 6 c ; the top of the air- 

 chamber is secured by a ring, H, clamped to the upright, K. Wrapped round the 

 air-chamber, to within two or three inches of each end, was a considerable length of 

 cotton-covered copper wire, ^th of an inch in diameter, and well soaked with shellac 

 varnish. The copper wire was wound round the chamber in one layer, thus forming 

 a magnetising solenoid in which there were 8 '25 turns in a centimetre ; since the wire 

 to be tested was well within the solenoid, the magnetising stress may be regarded as 



* ' Phil. Trans.,' 1886 (vol. 177, Part II.). 



