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duced, but in a less marked manner, if the second mass of air or membrane 
has a higher pitch than the first. The pitch of a membrane, on the other 
hand, is lowered by bringing a solid body near it. In order that a layer of 
air, bounded on one side by a membrane and on the other by a plane 
parallel to it formed by a solid free around its edge, may be reinforced by a 
given sound, its thickness must be proportional to its length ; further, this 
thickness depends on the ratio which exists between the sound proper to 
the membrane and the given sound, and also on the nature and dimensions 
of the membrane. We can, with sounding tubes with flute embouchure, 
reproduce the principal phenomena obtained with singing flames. The pitch 
of a pipe falls when we bring a solid body near its orifice. This flattening 
is still produced when the pipe is the centre of a solid plane which extends 
indefinitely around the pipe. 
Electrical Polarisation . — A great number of experiments on the electrical 
currents accompanying the non-simultaneous immersion of two mercury 
electrodes in various liquids are described in detail by M. G. Quincke, who 
has arrived at the following conclusions : If two mercury electrodes, con- 
nected by the wire of a multiplier, be immersed one after the other in any 
liquid which is a conductor of electricity (water, alcohol, saline solutions, 
&c.), an electric current is observed passing from the freshly wetted mercury 
surface through the liquid to the other mercury surface. The strength of 
the current diminishes as the resistance of the liquid column between the 
electrodes is increased. The electromotive force varies with the nature of 
the liquid and increases as the concentration diminishes, in some cases 
amounting to 0-6 of a Volt. The electromotive force increases if the 
boundary surface of mercury with the surrounding liquid in the last im- 
mersed electrode is more quickly produced. It soon, however, reaches a 
maximum, especially in the case of viscous liquids like glycerine. The 
cause of these currents is probably the alteration in molecular condition 
(change of density or concentration), which is gradually accomplished in 
the liquid near the surface of contact after the wetting. 
Curious Effect of Flame on an Electric Spark . — A curious effect of a gas 
flame on the current of a Holtz machine has been recently noticed by 
Mr. S. J. Mixter, and is recorded in “ Silliman’s American Journal ” for 
January 1875. The jet consisted of a glass tube drawn out to a point, and 
the flame had a length of about an inch and a diameter of only an eighth 
of an inch. Inserting this between the two terminals of the machine, the 
length of spark obtainable was at once increased from less than ten inches 
to over twelve, the full distance to which the balls could be separated. 
The same increase was not obtained by simply inserting a conductor between 
the two terminals, a ball an inch in diameter only lengthening the spark 
about an inch. 
Metallic Sulphides and their Electric conducting Power . — In a number of 
the u Academy ” for March appears the following note on this subject: — 
Apropos of a paper which appeared recently in “ Pogg. Ann.,” and was 
noticed in the “ Academy ” (Jan. 30), on the behaviour of iron and steel 
bars in a galvanic circuit, M. F. Braun, in “ Pogg. Ann.” (cliii. p. 557), gives 
an account of certain curious phenomena connected with the passage of 
electric currents through natural and artificial metallic sulphides. The 
