Chemistry. » 349 



noise in the air as they vary their colours or position, which may probably 

 be owing to the want of perfect silence at the time they made their obser- 

 vations on these meteors. I can positively affirm, that, in still nights, I have 

 frequently heard them making a rustling and crackling noise, like the wav- 

 ing of a large flag in a fresh gale of wind." It is probable that these lights 

 are sometimes much nearer the earth than at others, and this may have an 

 effect on the sound. — Quoted in the Dublin Phil. Journal, No. v. p. 419. 



GALVANISM. 



12. Galvani's First Experiment on the Frog; made in 1700.— The fol- 

 lowing curious fact is recorded in the History of the Academy of Sciences 

 for 1700, p. 40. " M. Verney showed, upon a frog newly dead, that, by 

 irritating a little with the scalpel, the nerves which go to the thighs and 

 legs, those parts make a noise, and suffer a species of convulsion. He af- 

 terwards cut the same nerves in the belly, and keeping them a little stretch- 

 ed with his hand, he made them produce the same effect by the same mo- 

 tion of the scalpel. This did not happen if the frog had been long dead." 

 — Zach's Corr. Astron. vol. xiv. p. 379. 



PNEUMATICS. 



13. Mr Ivory on the Heat extricated from Compressed Air. — From an 

 ingenious analysis, Mr Ivory has deduced the following proposition. " The 

 heat extricated from air, when it undergoes a given condensation, is equal 

 to three-eighths of the diminution of temperature required to produce the 

 same condensation, the pressure being constant. 



Air, under a constant pressure, diminishes r^th of its volume for every 



degree of depression on Fahrenheit's scale ; and, therefore, one degree of 

 heat will be extricated from air when it undergoes a condensation equal to 



480 8 480 

 If a mass of air were suddenly reduced to half its bulk, the heat evolved 



would be - -f- ^ = 90°.— Phil. Mag. No. ii. p. 74. 



II. CHEMISTRY. 



14. Letter of M. Gaultier de Claubry to M. Gay-Lussac on the mode in 



which Alkaline Chlorides act in purifying an Infections Atmosphere, 



The object of this letter is to prove experimentally, that the explanation 

 given by M. Gay-Lussac in the 26th volume, page 165, of the Annates 

 de Chimie et de Physique, is correct. M. Labarraque, who has paid par- 

 ticular attention to the subject, supposes that the putrid miasms them- 

 selves are absorbed by the solution of the chloride, and then decompos- 

 ed by the chlorine which is present. M. Gay-Lussac, on the contrary, 

 conceives that the chlorine is disengaged by the carbonic acid of the air 

 or by that emitted by the putrefying substances. In this way, a carbo- 

 nate of the alkali is gradually generated, chlorine is set free, and then pro- 

 duces its effect, by being mixed with the atmosphere. M. Gaultier de 



