Electricity^-'Chemistry, 87^ 



they form on the ceiling. This image is not circular, but polygonal, on 

 account of the undulating motion of the reflecting plate, and the angles of 

 the polygon are seen oscillating round fixed positions, or turning in a 

 continuous manner — Le Globs, August 2, 1827. 



15. M, Savart on Normal Vibrations. — An interesting memoir by M. 

 Savart on this subject was read at the Academy of Sciences on the 13th 

 August. It is well known that sounding bodies emit several sounds at 

 once, and consequently that they are the seat of several modes of division 

 that are superimposed. Among these co-existing modes of division, M. 

 Savart shows that there is always one which is more strongly and distinct- 

 ly marked than the rest. In order to show this, he throws lycopodium 

 and sand, dry, but not too fine, upon the sounding body. The sand de- 

 lineates the principal mode of division, and the fine dust the co-existing 

 modes of division, in which the amplitudes, and the oscillations of the vi- 

 brating parts are the greatest possible. From the principal figure, M. 

 Savart can predict the secondary acoustic figure, and vice versa. He re- 

 gards the secondary motions as the cause of the timbre of different sono- 

 rous bodies, and he supposes that the nodal, helicoidal lines which he has 

 observed on the faces of bodies vibrating longitudinally, are only the traces 

 of a secondary mode of division, an opinion which, if confirmed, will throw 

 light on one of the most obscure and curious points of acoustics.— Le 

 Globe, August 23, 1827. 



ELECTRICITY. 



16. M» Becquerel on the Electricity from the pressure of two bodies, and 

 the cleavage of crystals. — In a memoir on this subject, read at the Academy 

 of Sciences on the 6th August, M. Becquerel shows, that, if we press two 

 bodies against each other, and afterwards diminish the pressure, and again 

 augment it, these bodies, in being freed from the pressure, never carry off" 

 with them any more than the quantity of electricity relative to the strong- 

 est pressure, so that the partial frictions which the particles experience 

 during these pressures of unequal intensity produce no modification in the 

 developement of electricity. 



M. Becquerel also shows that a great number of substances produce, by 

 rapid cleavage, the same electric phenomena as mica and sulphate of lime. 

 He shows also, that when the separated laminae are again brought together 

 and slightly pressed, they produce the same effects as by cleavage. Here 

 the pressure produces the same phenomena as the force of aggregation 

 He then shows that in the topaz the species of electricity acquired by each 

 plate, at the time of the cleavage, is not owing to the position of the plate in 

 reference to the axis of the crystal, but to the nature of the vibration of 

 ia molecules.— Zre Globe, 23d August 1 827. 



II. CHEMISTRY. 



i 7. Dr Christison on the Taste of Arsenic, and on its property of pre- 

 serving the Bodies of Persons who have been poisoned iviih it. (From 



