218 
TOPULAR SCIENCE REVIEW. 
Experiments were made by reversing the ventilating valves, and these- 
showed distinctly that good or confused hearing depended very materially 
on the amount and direction of the air-currents circulating in the area. 
Electromagnetic Rotation of the Plane of Polarisation in Vapour of Sulphide 
of Carbon has been investigated by Kundt and Rontgen. Faraday failed to- 
detect this phenomenon in gases generally. An iron tube was closed at the 
ends by glass plates and surrounded with a steam-chamber. This latter 
was enclosed in six large coils of wire traversed by the current from sixty- 
four large Bunsen cells. The temperature was then raised to that of boiling 
water, and a pencil of polarised light was extinguished by a Nicol’s prism as 
analyser. On passing the current the field brightened distinctly, and stilt 
more by commutation of the current. This rotation followed the direction 
of the positive current, and amounted to about 30' of arc. 
The same rotation was afterwards observed in gaseous sulphurous acid at 
100° C., and at a pressure of twenty atmospheres ; also in sulphuretted 
hydrogen at the same pressure, and at the ordinary temperature. Air up to 
twenty-five atmospheres gave no results. 
Velocity of very Loud Sounds. — Mr. W. W. Jacques communicates some 
experiments on this subject to “ Silliman’s Journal,” from which it appears 
that — 
(1) The velocity of sound is a function of its intensity. 
(2) Experiments in which a cannon is used contain an error, probably due 
to the bodily motion of the air near the cannon. A low musical sound should 
be used for determinations of velocity. 
A Current Regulator. — Dr. Siemens brought before the Royal and Physical 
Societies an instrument of this character, depending for its action on the 
heating effect of the current. In the earlier form of apparatus a fine strip of 
metal, rolled very thin, was attached at one end to a rigid support, carried 
over a pulley, and fixed at its other extremity to a lever connected with a 
series of contact pieces joined to resistance-coils. 
In the later form a similar strip of mild steel was stretched across the 
bottom of a cylindrical box, carrying in the middle a sliding bar or pin resting 
by its end vertically on the strip. According to the expansion of the strip by 
the heat of the current, the pin is depressed or elevated, and a circular 
series of short resistance-coils is introduced one by one into the circuit. 
The included resistance is thus increased by a rise and diminished by a fall of 
temperature in the sensitive slip. Dr. Siemens, in describing this compen- 
sating action, said : “ Suppose that the current intended to be passed through 
the instrument is capable of maintaining the sensitive strip at a temperature 
of, say, 60° C., and that a sudden increase of current takes place, in con- 
sequence either of nn augmentation of the supply of electricity, or of a change 
in the extraneous resistance to be overcome, the result will be an augmentation 
of temperature, which will continue until a new equilibrium between the heat 
supplied and that lost by radiation is effected. If the strip is made of metal 
of high conductivity, such as copper or silver, and is rolled down to a thick- 
ness not exceeding 0*06 mm., its capacity for heat is exceedingly small ; and 
its surface being relatively very great, the new equilibrium between the 
supply of heat and its loss by radiation is effected almost instantaneously. 
But with the increase of temperature the position of the regulating lever 
