174 Dr. A. M. Mayer's Researches in Acoustics. 



the bar, B, rests in slots in the supports, S, S'. The tube T 

 is slightly shorter than the bar B. Washers of rubber (shown 

 in black in the figure), of the same diameter as the outside 

 diameter of the tube, are placed in the screw- caps, C, C. 

 These washers are perforated with holes of diameters smaller 

 than the thickness of the bar. When the caps are screwed up, 

 the rubber washers press against the ends of the bar. This 



Fiar. 2 



pressure is further increased by flat rings which surround the 

 holes in the washers, and are pressed against these washers by 

 means of the springs, D, D'. By this arrangement the sur- 

 faces of the ends of the bars are exposed, while the contact 

 of the washers on the bars makes a water- and steam-tight 

 joint. Thus the bar may be surrounded with ice, or with 

 steam, or with a current of water of different temperatures, 

 and be cooled or heated up to its terminal planes, while the 

 holes in the washers allow the micrometer-screws, M, M', to 

 be brought to contact with the terminal planes of the bar. 

 Two helical springs are attached to the column A. The 

 other ends of these springs are fastened to rods projecting 

 from the tube T. Thus the same pressure of contact is always 

 made between the bar and the end of the micrometer-screw M. 

 The tube T is supported in Vs, V, V, and the greater part of 



