130 Analysis of Scientific Books. 



cooling, and specific heat, all naturally belong to one head, — 

 the dislribution of this power. Expansion (or, in its general 

 enunciation, change of volume) and change of state are two of 

 its effects. As to the nature of heat, Dr. Thomson was well 

 aware that he had no definite inl'criiiation to communicate. 

 Its sources scarcely require a distinct section, for they would 

 spontaneously spring out of the previous' discussions, if they 

 were skilfully handled. He has at last discarded the whole of 

 liis speculations, concerning the absolute quantity of heat 

 in bodies, or the natural zero, and we wish he had applied the 

 same salutary pruning to his preface on combustion. His 

 table of the expansions of air, in which unity is placed at 32° 

 and 1.375 at 212°, is of no use to the practical chemist. It is 

 merely a transcript from that rare work, called A Readi/ 

 Reckoner, the tables of which the Doctor seems fond of re- 

 printing ; for in his Annals for August, 1817, we find columns 

 containing many hundred figures, which run thus : if 1 gives 

 8, 2 will give 16 ; 3, 24 ; 4, 32 ; 5, 40 ; and so on, up to the 

 fatiguing length of 300 multiplications of the number 8. Most 

 readers would be satisfied with one century of such inventions. 

 Whenever the Doctor generalizes on his own bottom, he 

 constantly sinks into downright absurdity. Thus ; " But if this 

 explanation be correct, those bodies ought to expand most, 

 whose attraction of cohesion is least*." Now observe, that in 

 the very same section, his expansion tables concur in proving, 

 that all the metals expand more than glass, therefore their 

 " attraction of cohesion is least." Mr. Rennie has shewn, that 

 wrought iron, has a cohesive attraction three times greater than 

 cast iron ; therefore by Dr. Thomson's laiu, the latter should 

 expand most ; whereas it certainly expands least. Cast cop- 

 per and cast iron have the same cohesive force, according to 

 Mr. Rennie's accurate experiments ; yet by Dr. Thomson's 

 tables, the former expands more than the latter in the ratio of 

 19 to 11, instead of being equal, agreeably to his laiv. To 

 the Avant of the comparing faculty (or organ of inductiveness) , 

 we must ascribe the perpetual contradictions which we meet 

 with in this system. Thus in transcribing the results of Dulong 

 and Petit on expansion, he says, " Difterent glass tubes from 

 different manufactories gave precisely the same result f." And 

 at the bottom of the next leaf, he says, " But different kinds 

 of glass differ so much from each other (in expansion), that no 

 general rule can be laid down." His account of the thermometer 

 is contemptible. He gives no directions whatever, by which an 

 accurate thepjnometer may be made, or by which its indications 

 may be verified ; but, after some historical notices, concludes 

 his discussion of this important instrument, with the common 



* System, 6th Edit. I. 30. f Cth Edit. I. 34. 



