420 



NATURE 



\ April 2, 1874 



figures and describes several of the Chelonia and other 

 reptiles which come from the same locaHty. 



The above notice of the results arrived at by American 

 men of Science show that they deserve the careful study of 

 English pateontolologists and geologists, as they have 

 already thrown great light on the fauna of the Tertiary 

 period, and give promise of adding much more to our 

 knowledge of that epoch, so important to the student of 

 the anatomy and classification of the higher vertebrata. 



OUR BOOK SHELF 



The Laboratory Guide, a Manual of Practical Chemistry 

 for Colleges and Sc/iools, specially arranged for Agri- 

 cultural Students. By Arthur Herbert Church, M.A. 

 (London : Van Voorst, 1874). 

 Teachers of chemistry will be glad to welcome the 

 third edition of Prof. Church's " Guide," to which much 

 new matter has been added. Being specially adapted for 

 students of agricultural chemistry, the book is necessarily 

 somewhat limited in its scope, but the amount of informa- 

 tion conveyed within the small compass of 215 pages is very 

 great, and is moreover lucid and accurate. The book is 

 divided into three portions, the first treating of a chemical 

 manipulation, the second of qualitative analysis, and the 

 third of quantitative analysis. The author's preliminary 

 remarks upon manipulation are excel'ent, and should be 

 graven upon the miad of every chemical student. In the 

 " Introduction " we are told that the student " must never 

 forget that the experiment is the- means, not the end. 

 .... Merely to make a coloured precipitate or a flash 

 of bright flame is not the end of experimenting." 



These remarks are much to the purpose, and we 

 commend them to the notice of chemists of older growth, 

 as well as to beginners. The sudden introduction of 

 equations on p. 8 without any previous explanation of 

 the meaning of symbolic formulae appears somewhat 

 unsystematic, but the student is recommended by Prof. 

 Church to attend some course of lectures on inorganic che- 

 mistry, and to study the corresponding chapters in 

 Roscoc's Chemistry, at the same time that he is working 

 through the " Guide." As the " Guide " is at present 

 arranged, the student will find this absolutely necessary. 

 The classification of the metals adopted by the author 

 calls for remark — iron and manganese are classed as 

 dyads and aluminium as a triad. Further on it is ex- 

 plained that this last metal is only a pseudo-triad, being 

 in reality a tetrad. Why not class it with the tetrads at 

 once ? Hexad metals and pentad metals are ignored 

 altogether, although manganese forms a hexafluoride, 

 arsenic, and antimony, penta-haloid compounds, &c. We 

 must protest also against the use of the words " vinculant,' 

 " vinculance," " univinculant," &c. No advantage is 

 likely to accrue to the science from this new phraseology, 

 and the terms "atomicity," "monatomic," " diatomic," &c., 

 which are in general use, express the idea perfectly. The 

 tables for qualitative analysis differ but little from those 

 generally adopted. The quantitative processes for the 

 analysis of natural products, soils, foods, &c., will be found 

 very useful. In addition to the direct benefit arising from 

 the issue of books like the present, there is an indirect 

 benefit for which we ought to be also indebted to Prof. 

 Church — we refer to the expulsion from the market of 

 hastily compiled and inaccurate works by so-called 

 " Science Teachers," such as it has been our duty to 

 condemn on former occasions. 



LETTERS TO THE EDITOR 

 [The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. No notice is taken of anonymous 

 communications. ] 



Prof. Tail and Mr. Spencer 

 As is shown by the passage from his Thermodynamics which 

 he re-quotes, Prof. Tait holds that " Natural philosophy is an 



experimental, and not an intuitive science. No h priori rea- 

 soning can conduct us demonstratively to a single physical 

 truth." 



I hold, on the contrary, that as there are a, priori mathe- 

 matical truths, the consciousness of which results, not from our 

 individual experiences, but from the organized and inherited 

 effects of ancestral experiences, received throughout an immeasur- 

 able past ; so are there li priori physical truths, our consciousness 

 of which has a like origin. 



I have endeavoured to show that Prof. Tait himself, by saying 

 of physical axioms that the appropriately-cultivated intelligence 

 sees "at once" their "necessary truth," tacitly classes them 

 with mathematical axioms, of which this self-evidence is also the 

 recognised character. Further, I have contended that the laws 

 of motion are u priori truths oi this kind ; arc enunciated by 

 Newton as such ; are adopteii from him by Prof. Tait ; and are 

 not furnished by Prof. Tait with any such e.xperimental proofs as 

 he asserts are needful for the establishment of physical truths. And 

 I have gone on to show that no experimental proofs of them are 

 possible — that every supposed proof, whether derived from terres- 

 trial phenomena or from celestial phenomena, involves a petitio 

 priiicipii. 



In the course of the discussion I have examined the reason 

 Prof. Tait gives for asserting that the laws of motion are 

 not to be accepted as valid ii priori. The reason is that "as the 

 properties of matter might have been such as to render a totally 

 different set of laws axiomatic, these laws must be considered as 

 resting on convictions draiin from observation and experiment^ 

 and not on intuitive perception. " 



The worth of this reason I have tested by asking the origin 

 of Prof. Tait's professed knowledge that "the properties of 

 matter might have been " other than they are. Here is the 

 passage : — 



" It will suffice if I examine the nature of this proposition that 

 ' the properties of matter might have been ' other than they are. 

 Does it express an experimentally-ascertained truth ? If so, I 

 invite Prof Tait to describe the experiments. Is it an intuition ? 

 If so, then along with doubt of an intuitive belief concerning 

 things as they are, there goes confidence in an intuitive belief 

 concerning things as they are not. Is it an hypothesis ? If so, 

 the implication is that a cognition of which the negation is in- 

 conceivable (for an axiom is such) may be discredited by inference 

 from that which is not a cognition at all, but simply a supposi- 

 tion. Does the reviewer [a critic whose attack I was answernig] 

 admit that no conclusion can have a validity greater than is 

 possessed by its premises? or will he say that the trustworthiness 

 of cognitions increases in proportion as they are the more in- 

 ferential ? Be his answer what it may, I shall take it as unques- 

 tionable that nothing concluded can have a warrant higher than 

 that from which it is concluded, though it may have a lower. 

 Now the elements of the proposition before us are these : — As 

 ' the properties of matter might have been such as to render a 

 totally different set of laws axiomatic ' \therci'ore'\ ' these laws 

 [now in force] must be considered as resting . . . not on intui- 

 tive perception : ' that is, the intuitions in which these laws are 

 recognised, must not be held authoritative. Here the cognition 

 posited as premiss, is that the properties of matter might have 

 been other than they are ; and the conclusion is that our intui- 

 tions relative to existing properties are uncertain. Hence, if 

 this conclusion is valid, it is valid because the cognition or intui- 

 tion respecting what might have been, is more trustworthy than 

 the cognition or intuition respecting what is ! Scepticism re- 

 specting the deliverances of consciousness about things as they 

 are is based upon faith in a deUverance of consciousness about 

 things as they arc not ! " 



From this passage Prof Tait has quoted a small part 

 which, standing by itself, appears somewhat strange ; but which 

 ceases to appear strange when read along with the rest. In 

 seeking the authority which Prof Tait has for asserting that 

 " the properties of matter might have been" other than they 

 are, I have tried all possible suppositions ; and as he professes 

 to have faith only in experimentally-ascertained truths, I have 

 asked whether this is one ; by way of showing, unmistakeably, 

 that in the absence of experimental warrant he must admit it to 

 be, if not a mere hypothesis, then an intuition. Whence results 

 the incongruity I have pointed out. 



Prof. Tait says this argument of mine reminds him of a student 

 whose conceptions of algebraic processes were shown by asking — ■ 

 "But what if x should turn out after all not to be the unknown 

 quantity ? " His imagination suggests to Prof Tait an analogy 

 too remote for me to perceive ; and one which I think few wiU 



