!i64 Dr. Thomson's Answer to the Review of the [April, 



considered the mechanism of expansion ; and that ignorance of 

 a subject does not deter him from writing on it. 



I cannot avoid noticing a most extraordinary passage in the 

 same page of the Review. A paper exhibiting the strength of 

 alkahes, drawn up by Mr. Charles Tennant, of St. RoUocks, 

 Glasgow, is inserted in the Annals of Fhilosop/n/f vol. x. p. 115, 

 with the author's name attached to it. This paper the Reviewer 

 ridicules in such a way that every reader must suppose that I 

 was the author of it. Now, in the first place, the table is an 

 accurate one ; and Mr. Tennant, who drew it up, is entitled to 

 great credit for his sagacity; for he had deduced the true atomic 

 weights of potash and soda (6 and 4) from his own experiments 

 several years before they had been recognised by any scientific 

 chemist. It was this circumstance which drew my attention, 

 iind induced me to insert the paper, in order to secure for Mr^ 

 Tennant that priority to which he was justly entitled. The table 

 was intended for the bleachers only, and I have had the means 

 of knowing that it has been of great use to them. But suppos- 

 ing that the paper had been tritiing and useless, what had that 

 to do with my System of Chemistry ? Have no trifling papers 

 appeared in the Journal of the Royal Institution? 



3. Thermometer. — The Reviewer affirms that my account of this 

 instrument is contemptible. I have had the curiosity to look into 

 Mr. Brande's account of it, and find it nearly the same as mine. 

 It certainly contains nothing more than mine does. The 

 Reviewer conceives that I should have given an account of the 

 mode of making these instruments. If he will come and attend 

 a course of my lectures in the University of Glasgow, he will 

 have an opportunity of hearing a minute detail of every thing 

 that I know respecting the making and use of this very import- 

 ant instrument. But such details would have been inconsistent 

 with the nature of my System of Chemistry. I might as well 

 have given a minute account of the mode of making crucibles, 

 retorts, mirrors, air-pumps, electrical machines, hammers, anvils, 

 and stone jugs. I might in this way have swelled out my book 

 to the size of an Encyclopaedia ; but I should have rendered it 

 much less adapted to the student of chemistry than it is. 



4. Galvanic Batterjy, — I have ** repeated the gross blunder 

 which, in our former critique, we pointed out relative to the 

 energy of the pile, which he very ignorantly says, ' at least as far 

 as chemical phenomena are concerned, '* increases in proportion 

 to the size of the pieces.'" — (Review, p. 136.) That this state- 

 ment was not the effect of ignorance must be known to all who 

 have attended my lectures in Glasgow. I have an apparatus for 

 the purpose of showing that the heat, and consequently the 

 action of the pile upon metals, depends upon the size of the 

 plates ; and that thick wires may be melted by a battery which 

 aeither gives shocks, nor decomposes water, nor ignites char- 



