272 The Progress of Physical Discovery. [MARCH, 



not the case in Sweden and Russia ; and in the winter the west winds 

 are more southern, whilst they are more direct, or more to the north, 

 during the summer. 



The celebrated Chladni, whose recent loss will be deplored, not only 

 in Germany, but by all who feel the importance of the study of the 

 supreme law of nature by the analogy of its different elements, shewed, 

 many years since, that the vibrations of sounds put into motion grains of 

 sand, united on a glass plate, in such a manner, that when the tones are 

 pure the grains unite in regular forms, and when they are discordant, 

 the grains trace upon the glass figures without symmetry. His latest 

 discovery, previous to his death, was that of the manner of the propaga- 

 tion of sound, by means of applying the theory of liquid waves to that of 

 aerial ones. When a sonorous bar of metal or glass is plunged into a 

 liquid surface, four currents are observed round this bar, two of which 

 are in the direction of the vibratory movement, and the others perpen- 

 dicular to the direction of the former. Two currents are excentric or 

 flying, and two concentric or returning, and between them is formed an 

 oval movement ; and from these phaenomena we may imagine what 

 passes in the waves of the air, and explain the interruption of sound in 

 certain directions where the waves take a transverse course, viz. when 

 they pass from the centrifugal to the centripetal movement. Nothing is 

 so highly satisfactory as this analogy when shewn to exist in different 

 elements, an analogy which it has been the especial merit of the Ger- 

 mans, and of none more than Chladni, to inculcate as one of the funda- 

 mental principles to be borne in mind in the study of nature. 



Schabler's examination of the temperature of vegetables has ascer- 

 tained the singular fact, that trees have always, at sun-rise, a higher 

 temperature than the surrounding air ; whilst in the afternoon, when the 

 air is become hotter, their temperature is less. This is the case not only 

 in summer, but also in the midst of winter, and even when the thermo- 

 meter is constantly below zero. Vegetables always keep up a moderate 

 temperature, which is best explained by their being bad conductors of 

 heat, and which, their being fixed in the ground, tends to keep in a 

 uniform state. 



M. Robiquet had discovered, in liquorice root, a crystalline matter to 

 which he had given the name of agedoite, and Vauquelin had found, in 

 the juice of asparagus, a substance which he called asparagine. It was 

 now ascertained by M. Plisson, that these two are, in all respects, iden- 

 tical substances, and not other, or different. Berzelius's examination of 

 tannin, of gelatine and albumen, of copal, and gum lac, or liquorice 

 sugar and amber, are equally valuable with the former researches of 

 this distinguished chemist. In addition to the chromic acid of an 

 orange colour, already brought to light by Vauquelin, M. Kcechlin now 

 detected another acid in chromium of a green colour, imparting to acid 

 salts a greenish violet, and to neuter salts a green hue. The influence of 

 electricity, on the emission of odour, was perceived by M. Libri, who 

 found, that when a current of electricity crosses an odoriferous sub- 

 stance, its scent becomes weaker and weaker, and at last entirely disap- 

 pears ; and many substances, as camphor, for example, do not resume 

 their qualities of scent for a considerable time afterwards. M. Prevost 

 has lately advanced the theory, that whiteness is only a relative sensa- 

 tion, depending upon the predominating light. Two lights, that of the 

 day, and of a candle, when seen separately, appear white ; when brought 



