188 ^'WiW Mr. iihUdren'sSiimmarif View of [March, 



munications were read before the Royal Society in 1808, the 

 former on the 14th of January, the latter on the 28th of the 

 same month. Berzehus justly remarks, that this discovery may 

 be considered without exaggeration as one of the greatest steps 

 that chemistry has ever made towards perfection, and that the 

 honour of the invention of the doctrine oi multiple propcnt ions is 

 due to Dalton alone. 



In 1806, MM. Gay-Lussac and Humboldt found that one 

 volume of oxygen gas combines with two volumes of hydrogen 

 gas to form water, and the first of these two philosophers some 

 time after discovered that gaseous bodies in general combine 

 according to certain fixed laws, and that one measure of one gas 

 unites either with half a measure of another, or with 1, 2, 3, &c. 

 measures ; or, in other words, that gases either combine in equal 

 volumes, or the volume of one gas is a multiple by a whole num- 

 ber of that of the other. M. Gay-Lussac published a valuable 

 paper on this subject, entitled Memoire siir la Combiiiaison des 

 SuLsicaices Gazeiises, les imes avec les autres, in the second volume 

 of the Memoires tie la Societe d'Aicueil, in the year 1809. 



If we substitute the word atom for that of volume, and imagine 

 the substance to be in the solid instead of the gaseous state, 

 Gay-Lussac's theory coincides exactly with Dalton's, and is a 

 direct proof in confirmation of its truth. 



In 1812, Sir Humphry Davy published his Elements of Che- 

 mical Philosophy,* m the sixth section of the first division of 

 which work he has given a general view of the theory of definite 

 proportions, and iu a variety of other places has shown its 

 importance in calculating the results of chemical action ; and 

 since that period many of the first chemists in Europe have 

 attentively studied the atomic theory, and have confirmed it, by 

 a multitude of valuable experiments : amongst the most conspi- 

 cuous in this field of inquiry are Thomson and Berzelius. 



When we reflect on the cause of chemical proportions, the 

 most probable idea that presents itself to our imagination is, 

 that all bodies are composed of elementary particles or atoms, 

 incapable of mechanical division,^ and which unite together in 

 such a manner, that an atom of one element combines with 

 1, 2, 3, &c. atoms of another element. With this simple postu- 

 late, to which the mind readily accedes, it is easy to explain all 

 the phenomena of chemical proportions, especially those which 

 we call multiple proportions. By the union of two or more 

 elementary atoms, compound atoms are formed which are as 

 incapable of mechanical division as the former, and these again 

 unite together to form atill more compounded atoms, and so on 



* Is it always to be a source of regret, that only the first part of that invaluable work 

 has seen the light? 



+ On thi subject of the limited diTisibility of matter, see Dr. WoUaston's beautiful 

 paper " On the Finite Extent of the -Atmosphere."— (Phil. Trans, for 1822, p. 89.) 



