542 



Mr. G. F. Rodwell. 



extent of half a single coil, it moved the index through its entire 

 range, viz., from 0° to 180° of arc. By this means any possibility of 

 the chain doubling upon itself was obviated. 



6. But perhaps the most important changes were the removal of 

 stuffing boxes I and the rods H from the trough F, and the substitu- 

 tion of levers working over the rim of the trough ; and the suspension 

 of the rod of substance under examination in a cradle between the 

 fevers. This was effected in the following manner : — 



Section through the trough longitudinally, showing the mode of suspension of the 

 bar, and the position of the levers. 



A horizontal bar LL (fig. 4) was supported by rods N, N, strengthened 

 by cross bars (not shown) let into the stone base of the instrument ; 

 it carried Y-shaped brass levers B, B, moving about axes at C, C (figs. 4 

 and 5), attached at the points A, A. F is the trough in which hot 

 ceresine is used for heating the bar under examination, H, supported 

 by the cradle G. Two rods I, I, which slide in holes K, K, and are 

 capable of being held at any height by screws, support the cradle G. 

 D is the rod (figs. 1 and 2) which bears upon the lever S, and M the 

 point of the micrometer screw. 



The apparatus was standardised at frequent intervals by the use of 

 a rod of fine homogeneous silver. Ceresine boiling at 430° C. was 

 used to heat the rods in F, and it was heated to any desired tempera- 

 ture by means of a Bunsen burner placed beneath, and near the centre 

 of the trough. 



