1830.] The Progress of Physical Discovery. 271 



specific heat diminishes with the pressure, and equally as to all the 

 gases, following a progression slightly convergent, and in a proportion 

 much less than that of the pressure and that each gas has a different 

 conducting power, that is, that all gases have not the same power of 

 communicating heat. Mr. Perkins's cylinder for the compression of 

 water, as applied to his steam-gun, is too well known to require descrip- 

 tion here ; and Mr. Oersted's researches on the relative compressibility of 

 different fluids at high temperatures have established the following rules 

 on that subject, viz. : 1st. That the compression of water is proportionate 

 to the compressing forces, that produced by an atmosphere being nearly 

 45 millionths of the volume ; 2nd. That relatively to the temperature of 

 water compressed as far as 48 atmospheres, no heat is disengaged by 

 this compression; 3rd. That the compressibility of mercury seldom 

 exceeds a millionth of its volume for each atmosphere ; 4th. That that 

 of sulphuric ether is about three times that of alcohol, twice that of sul- 

 phuret of carbon, and only once and one-third that of water ; 5th. That 

 the compressibility of water containing salts, alkalis, or acids, is less 

 than that of pure water ; and 6th. That the compressibility of glass is 

 excessively small and very inferior to that of mercury. Berzelius, in 

 this year, directed his attention to the component principles of indigo, 

 among which he recognized four perfectly sui generis, viz. a peculiar 

 substance of a glutinous nature ; a brown substance, neither acid nor 

 alkaline, having a great affinity for acids ; a red substance, which, with 

 alcohol, gives a beautiful red dye; and the blue of indigo, a matter 

 without taste or smell, and having neither acid or alkaline properties. 

 Liebig also produced from indigo, by the action of nitric acid, a yellow 

 bitter substance, which he judged to be an acid, and gave it the name of 

 carbazotic. Brome, which we have mentioned, has a strong analogy to 

 chlorine and iodium, and it is not, therefore, surprising that M. Serullas 

 should now have ascertained, that it forms similar combinations, and 

 produces hydrobromic aether, or cyanure ofbrome, in the same way as 

 cyanure of iodium is formed. It was this year first announced by Mr. 

 Walker, that for the excitement of electricity by contact there must 

 always be three bodies of a differently exciting power, and that all 

 phaenomena are subject to this condition. As, for instance, if two por- 

 tions of the same metal are put in contact, and electricity is produced, 

 it arises from there being three different states of temperature put into 

 action, and one of which is the result of the two others. What particu- 

 larly supports this idea is, that the electric currents are always the more 

 apparent, as a third more sensible state of temperature is produced. 



The spirit of inquiry had not, in any degree, relaxed in 1828, nor is 

 there any semblance of its stagnation in the present year. We learn 

 from Schouw's Observations on the Winds the most perfect information 

 hitherto ascertained with regard to their direction in the northern parts 

 of Europe. It is a general rule, that the west winds are more frequent 

 than the east ; but the west winds become rarer as they approach the 

 centre of the continent, being more frequent in England, Holland, and 

 France, than in Denmark or Germany ; and more so again in the latter 

 countries than in Sweden and Russia. At London the east are to the 

 west winds as 1 to 1-7 ; at Amsterdam as 1 to 1-6; at Copenhagen as 

 1 to 1-5 ; at Stockholm as 1, to 1-4; and at St. Petersburgh as 1 to 1-3. 

 In the western and central parts of the north of Europe, the west winds 

 are more frequent in the summer than in the spring or winter, which is 



