480 Miscellaneous Intelligence. 



bave a great analogy with each other. When plates of mica or 

 sulphate of lime are suddenly -separated, each surface is electrical, 

 the two being contrary to each other ; if they be put together 

 again, and slightly pressed, upon separation they exhibit the same 

 electrical phenomena as before. Hence the pressure which 

 mechanically causes the approximation of the particles produces 

 the same effects as tlie force of aggregation, which in reality only 

 occasions a more immediate contact of the same particles. 



Every substance, regularly crystallized, possesses the same 

 property as mica and sulphate of lime. To obtain the effect, it 

 is necessary that the cleavage be regular and perfect; if it be 

 irregular, some plates take one electricity and some another, and 

 the effects are no longer distinctly observed. 



The kind of electricity acquired by the different surfaces varies 

 according to circumstances not yet ascertained. The topaz has 

 only one cleavage, and that perpendicular to the axis of the crystal, 

 but no regularity is observed in the nature of the electricity j for 

 sometimes the surface towards one end and sometimes that 

 towards the other, takes the same electricity. — Annates de Chi- 

 mie, xxxvi. 265. 



11. On the Velocity of Sound in Water. — Experiments on the 

 velocity of sound in water have been made by M. CoUadon on 

 the Lake of Geneva, and are connected with researches by him- 

 self and Sturm on the compressibility of fluids. The space 

 through which the sound passed was about 45,000 feet (13487 

 metres). The sound was produced by striking a large bell 

 suspended in the water, and was heard by means of a peculiar 

 apparatus, so constructed that the person who listened for it 

 could also observe the signal at the bell, and both set going and 

 stop the time-piece. The mean of several experiments was 9.4 

 seconds, for the whole distance : on dividing the distance by the 

 time, the velocity of sound on the water of this lake was 1435 

 metres, or 4708 feet per second. 



The water being examined, gave one six-thousandth of its 

 weight of saline matter ; and its specific gravity at 40^: Fahr. was 

 1.00015. 



M. Colladon remarks that the sound of a bell heard at some 

 distance under water is strikingly distinct from that of the bell in 

 air, being a short, brief noise, similar to that produced by striking 

 two knives together. If the distance be increased, still the 

 character is preserved, and it is impossible to distinguish whether 

 the original blow is strong but distant, or nearer and weaker. 

 It is only within the distance of 200 metres that the ringing of 

 the bell is heard : in air the reverse of this takes place ; the blows 

 struck upon a bell are easy to distinguish near at hand, but at a 

 distance melt into one continuous sound. This phenomenon 

 depends upon the nature of the sonorous vibrations in water. In 

 fact, it is known that in the vibratory motion of a fluid the duration 



