134 ANNUAL OF SCIENTIFIC DISCOVERY. 



same salt can induce crystallization, a view necessitating our be- 

 lieving that ail salts capable of supersaturation are everywhere 

 present in the atmosphere. Some other experiments seem to show 

 that a supersaturated solution may remain unchanged for a long 

 time in an atmosphere saturated with the same salt. We must 

 probably conclude that supersaturated solutions really contain the 

 anhydrous salt in a state of unstable equilibrium, only requiring 

 a disturbance to cause it to assimilate water, and thus produce a 

 less soluble compound. Prof. Tomlinson, in a later paper, con- 

 siders oils and fatty matters as chemically clean when they con- 

 tain no matter foreign to their composition. The oils, however, 

 whether clean or not, seem to act as powerful nuclei when in the 

 form 'of thin films/ He also remarks regarding M. Gerney's views 

 that when that physicist so carefully prepared his nuclei as to be 

 absolutely free from salt, he also made them chemically clean. 



VELOCITY OF SOUND. 



M. Andre, in " Comptes Rendus," gives an account of some 

 experiments made by him relative to the velocity of sound in 

 water contained in a cast-iron conduit. Having the charge of lay- 

 ing a tubular conduit, which had to be tested by pressure when 

 filled with water, it occurred to him to make some fresh measure- 

 ments on the velocity of sound in that medium. The conduit con- 

 sisted of cast-iron tubes of 0.8 metre internal diameter and 0.02 

 metre thick, forming when joined a straight line of about 600 

 metres. The motions of the liquid were recorded by means of a 

 kind of pneumatic register, the disturbance communicating itself 

 to the air confined in a small caoutchouc tube, and thence to a 

 membrane of gold-beater's skin. A very delicate lever fastened 

 to this membrane indicated, by its oscillations, the slightest move- 

 ments of the liquid. The time was measured by means of a 

 tuning-fork, which inscribed its vibrations on the blackened sheet 

 of a registering cylinder. This tuning-fork gave for a tempera- 

 ture of 20, 256 vibrations per second. 



A series of experiments was first performed to ascertain the 

 velocity in air using the same apparatus, and producing the 

 sound by means of a pistol charged with one gramme of powder. 

 The shock communicated to the air of the conduit was propa- 

 gated through the whole length of the tubes, and then returned 



^? ^j ^j 



after reflection. At each successive departure and return, the 

 style of the membrane gave very distinct indications on the reg- 

 istering cylinder. 



The temperature of the air in the tubes was 40 at one end and 

 20 at the other, as they were laid in an open trench upon part of 

 which the sun shone. Taking these two numbers as extreme 

 limits of temperature, the velocity of sound ascertained when re- 

 duced to zero was, 



V zz: 326.60 metres, if temperature was 40 ; 

 V = 337.50 metres, if temperature was 20. 



It is certain that the first number must be nearer the truth than 



