A 



Q 



Q 



^^^^ 



e 



3 



f/i*? Investigation of Young's Modulus for Wires. 549 



It was found that the boiling of the water shook the 

 apparatus. To remedy this two vertical joists were screwed to 

 the wall side by side, about three 

 inches apart, each carrying two Fig. 14. 



elbow-pieces of the steam-pipe ; 

 the upper pair were connected 

 by a short piece of thick india- 

 rubber tube, and the outer ends F 

 were similarly connected to boiler *= 

 and delivery-pipe, another india- 

 rubber joint intervening between 

 the latter and the jacket. The 

 lower pipe was similarly supplied 



with these indiarubber joints, the nature of which is shown 

 diagrammatically in rig. 14. 



Even so, after the water had been boiling for some hours, 

 the u bumping " caused vibrations, but this was stopped by 

 putting into the water some fragments of pumice. 



By adjusting the pressure by means of the water-pump 

 the water was boiled at different temperatures between 45° (J. 

 and 100° C, and the apparatus was kept at constant tem- 

 perature within the jacket for any length of time, at least the 

 three thermometers remained stationary. For lower tem- 

 peratures alcohol serves. At present little use has been made 

 of intermediate temperatures, as the results of observations at 

 13° 0. and 100° 0. respectively have given so much material 

 for consideration. 



The source of light is a sodium flame placed behind an 

 aperture in a screen at the focus of a convex lens ; the 

 parallel beam thus obtained is reflected by a mirror at an 

 angle of 45° into the prism, and through an aperture in the 

 silvering of this mirror the fringes are viewed along the path 

 of the incident light. The lower of the two equal faces of 

 the prism is half-silvered, and is adjusted about '25 mm. 

 above and parallel to the fully-silvered upper surface of a 

 glass plane ; both plane and prism were specially worked by 

 Hilger. Between the light from these two silvered surfaces 

 the interference is effected, part of the pencil of light being 

 reflected from the lower face of the prism and part from the 

 upper face of the mirror, the relative retardation depending 

 on their distance apart. 



Results. — We may now consider the results of some of the 

 observations on (1) copper, (2) soft iron, (3) " silver" steel, 

 and (4) hard brass. 



As we are only concerned with changes in the elasticity it 

 Phil. Mag. S. 5. Vol. 47. No. 289. June 1899. 2 F 



