PHYSICS. 415 



They are the same whatever the position of the disk iu the tube. Two 

 vibrating cylinders give notes whose pitch is inversely as their linear 

 dimensions. If the disk is on the side where the water enters, the 

 number of vibrations given by the same cylinder is proportional to the 

 square root of the charge. The nature of the tube is without influence 

 on the pitch of the note. (.7. Phys.^ May, 1884, II, iii, 218.) 



i'J'eyreneuf, following Tyndall, has called attention to the facility with 

 which sound traverses the interstices of solid bodies when the air iu 

 them is continuous. If the conjugate-mirror experiment be repeated 

 with a thick sheet of cotton wool between the mirrors, the sound does 

 not seem to be sensibly altered iu intensity. Two such sheets may be 

 interposed without preventing a sensitive flame from showing agitation 

 when placed in the conjugate focus. A sheet of filter paper is equiva- 

 lent to two sheets of cotton. To prove how difficult it is to destroy 

 resonance, the author states that he has performed the reflection ex- 

 periment with one of the mirrors covered with cotton upon its reflecting 

 surface. {J. Phys., May, 1884, II, in, 209.) 



Neyreueuf has also cojitinued his researches on the transmission of 

 sound by gases, and now gives the results obtained with nitrogen 

 monoxide and dioxide, ammonia, and ethylene. With nitrogen mo- 

 noxide and air the ratio of the flame distances was as 1.32 : 1 as a mean, 

 a value identical with that obtained for carbon dioxide. For ammonia 

 and air the ratio of the flame distances was 1.46 in place of 1.42. No 

 differences were observed between air, nitrogen dioxide, and ethylene. 

 He has observed that the damping effect of solid particles is very 

 marked. By using a long inverted U-tube of rubber filled with hydro- 

 gen the author has shown that the sound is much less enfeebled than 

 when traversing the same thickness of air. (C. E., xcviii, 980, 1264, 

 April, May, 18S4.) 



Elsas has studied the laws of the forced vibrations of plates; /. e., 

 those which the plate is made to execute under the influence of a vibrat- 

 ing body in communication with it. The plate, circular in form, and 

 made of cardboard, gelatin, ebonite, &c., is fixed by its center to a sew- 

 ing needle iierpendicular to its plane. A flexible cord, stretched by a 

 MTight, is attached to the needle by one entl, and by the other to the 

 prong of a tuning-fork. By means of sand and lycopodium on the plate 

 the position of the nodes and venters could be determined. The results 

 siiow (1) tliat such a plate givjes the nodal figures of Chladni, the cen- 

 ter being a node; (2) that these figures never have an uneven number 

 of diametral nodal lines ; (3) that, while always even, these lines degen- 

 erate frequently into hyperbolic curves, the vertices of which are on the 

 same straight line; (t) that for the same reasons the nodal lines are 

 wanting in the central portions, but appear on the i^eriphery of the 

 plate; and (5) that the nodal lines of communicated vibrations never 

 cut each other. These results are iu accord with those })revious]y ob- 

 tained with membranes. {Wied. Ami., xix, 474; J. Phys., January, 

 1884, II, III, 33.) 



