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



Determination of the Densities of the Bars at 4°. 



The bar whose density was to be determined was immersed 

 in water at 4° for a couple of hours. The bar was then sus- 

 pended by a platinum wire in water at 4° and weighed. The 

 bar was then removed from the wire and a quantity of water 

 equal in volume to the volume of the bar was added to the 

 water in the vessel, and the platinum wire, now immersed 

 exactly as it was when the bar was attached to it, was weighed. 

 This weight, subtracted from the previous weighing, gave the 

 weight of the bar in water. Every precaution was taken to 

 prevent, by means of screens, the action on the balance of 

 the currents of cold air in the balance-case, which are pro- 

 duced by the constant descent of air from the sides of the 

 cool vessel. 



The Apparatus in which the Bars were Heated and Cooled. On 

 the precautions used so that one is sure of having the real 

 temperature of the bar when it is vibrated. 



The apparatus used to heat and cool the bar is shown in 

 fig. 3. In a brass box, C, is inclosed a box, C, containing 

 the bar, B, supported on its nodes, N, N, by threads held by 

 upright rods. From this central box two tubes, T, P, pass 

 through the outer box C. The inner box is made water-tight 

 and steam-tight by a rubber washer which is pressed between 

 the top of the box and its cover by means of screws. Through 

 the tube, T, the bar is vibrated by letting fall upon its centre 

 a rubber ball fastened to a light wooden rod. On the blow of 

 the ball it rebounds, and the rod is caught by the fingers in its 

 upward motion. The cork is then at once replaced in the 

 tube, T. The sound from the bar is conveyed to the ear, at 

 E, by means of a tube (fig e 4). One branch of this bifurcated 

 tube leads through a rubber tube to the pipe, P, of the box, 

 fig. 3. The other branch leads to the fork, F, the number 

 of whose beats per second made with the vibrating bar is 

 measured by a chronometer. The pipe, S, allows the steam 

 to issue when water is boiled in the box, C, by a gas lamp. 

 The flow of gas through this lamp was neatly regulated by a 

 stop-cock turned by a long lever. The box, C, is covered, 

 except at the bottom, with thick felt. 



To determine the frequencies of vibration of a bar through 

 a range of temperature from 0° to 100°, the following method 

 was used. The box, C, was filled with ice, surrounding the 

 inner box, C. It thus remained for an hour so that the 

 boxes were cooled down to 0°, and the moisture in the inner 



