90 Memoir of the late 



tions, which laid the basis of the Scottish legislation on 

 excise, and rendered him in after-life the arbitrator in many 

 important revenue cases. 4. He likewise invented his sac- 

 charometer, which is still used by the Scottish excise under 

 the title of Allan's saccharometer. 5. In 1807, he first 

 introduced to the notice of the world, in the third edition of 

 his " System," Dalton's views of the atomic theory, which 

 had been privately communicated to him in 1804. He did 

 not confine his remarks to mere details, but made many 

 important new deductions, and by his clear, perspicuous, 

 and transparent style, rendered the new theory soon univer- 

 sally known and appreciated. Had Bichter possessed such a 

 friend as Thomson, the atomic theory of Dalton would have 

 long been previously fully discovered, and attributed to Rich- 

 ter. In his papers on this theory, which occupied much of 

 his thoughts, from the mathematical precision which it pro- 

 mised to impart to the science, we find numerous suggestions 

 cautiously offered, which have often been subsequently exa- 

 mined and confirmed, or developed in another direction. 

 Thus, in August 1813, he states, that, according to the atomic 

 numbers then determined, " an atom of phosphorus is ten 

 times as heavy as an atom of hydrogen. None of the other 

 atoms appear to be multiples of -132 (the atom of hydrogen 

 at that time adopted by chemists), so that if we pitch upon 

 hydrogen for our unit, the weight of all the atoms will be 

 fractional quantities, except that of phosphorus alone." It 

 was undoubtedly this observation which caused Dr Prout to 

 make new inquiries, and to announce, in November 1815, the 

 view that the relation of phosphorus as a multiple of hydro- 

 gen, as detected by Thomson, may be general, connecting all 

 other atomic weights with that unit, a view now generally 

 adopted, and considered as a nearly demonstrated law. 



The existence of such mathematical relations Dr Thomson 

 was continually in the habit of testing at the conclusion of 

 his own researches, or in examining the experiments of 

 others. Any peculiarity of character in a substance hitherto 

 known, or in a newly-discovered body, he never failed to 

 point out in his " System ; " and innumerable instances have 

 occurred, and might be mentioned if our space admitted, 



