RECORDS. 621 



The second paper, by Dr. TuftS, gave the results of experiments 

 on the transmission and reflection of sound by such materials as 

 flour, sand, sawdust, shot, and a few different kinds of cloths. 

 It was stated that when sound waves strike against materials 

 pervious to air they act very much like a pneumatic pressure, 

 and that the amount of sound transmitted through such mate- 

 rials is inversely proportional to the resistance offered by the 

 materials to the passage of a direct current of air. The results 

 of the experiments upon the reflection of sound from the same 

 materials showed that those materials which transmitted the 

 greatest amount of sound reflected the least. The paper also 

 contained an account of some experiments in which the sound 

 waves had to pass through some pervious material, such as the 

 curtain upon a wall, and were then reflected back through the 

 same by the impervious wall. The results of these experiments 

 showed that there was greater reflection when the curtains were 

 of very porous or of very impervious materials, than when they 

 were of materials of medium porosity, such as velvet. 



In the discussion that followed, Professor Hallock suggested 

 the practical application to the improvement of the acoustics of 

 rooms which might result from these investigations, and the use- 

 lessness of, the method of stringing wires in large halls to break 

 up echoes which had been often advised but which was disproved 

 by these investigations. Mr. Dudley also spoke of the attempts 

 which had been made to obtain materials absorptive of sound to 

 deaden the noise in railroad cars. 



The third paper by Mr. Dudley was profusely illustrated by 

 lantern slides. These showed the loci of the center of gravity 

 of the counter-weights, crank pins and driving axles in running 

 locomotives. Some of the photographs showed the position of the 

 counter-weights in the driving wheels of running locomotives in ref- 

 erence to the stremmatograph under the rail. The counter-weights 

 added to locomotive driving wheels to balance the reciprocating 

 parts, crank pins, main and side connecting rods, when the loco- 

 motive is runnino;, besides rotatinsf around the axles, move alonef 

 the rails per revolution, a distance equal to the circumference of 

 the drivers. The locus of the center of gravity of the counter 



