344 Bay — Residual Viscosity on Thermal Expansion. 



of the same material, which are connected with it by"T'^ 

 joints at a short distance from its ends. 



These uprights are screwed into circular cast-iron plates, 

 which are rigidly fastened to the wooden base, pq. Stop-cocks 

 are inserted in the sides of the uprights near their lower ends, 

 at e and o. By means of caps on the projecting ends of the 

 bar, aa, and plugs in the lower ends of the uprights, 55, the 

 framework of piping is made water-tight, and, by connecting 

 one of the cocks, ^, 6>, with a source and the other with a sink, 

 a continuous flow of water throughout the length of the bar, 



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If the temperature of the water passing through the bar 

 remains constant, the bar will not be sensibly affected by the 

 currents of heated air rising from the jets beneath the bath, and 

 the length of any portion of the bar will remain constant. A 

 public main is a convenient source, and, for a reasonable time, 

 will supply a flow of water at a nearly constant temperature. 



The projecting ends of the bar, aa, serve as convenient sup- 

 ports for the telescopes, h and Jc, which are fastened thereto in 

 an adjustable manner, so as to allow them to be focussed upon 

 their respective mirrors, v and u. 



The solid whose expansion is to be observed is suspended in 

 the bath from the bar, aa, by light bent rods, while the levers, 

 s, X, are supported below the same bar, in their proper positions 

 at the ends of the solid, by brackets, c, c, cast in brass. These 



