222 



NATURE 



[January 7, 1892 



OUR BOOK SHELF. 

 Stones for Building and Decoration. By George P. 

 Merrill, Curator of Geology in the United States 

 National Museum. (New York : John Wiley and 

 Sons, 1891.) 



This work deals almost exclusively with the building and 

 ornamental stones of the North American continent, the 

 references to similar rocks in Europe and elsewhere being 

 usually meagre and sometimes disappointing. As an 

 account of the rocks of the United States which are of 

 economic importance as building materials, the work is, 

 however, a very admirable one ; and, as might have been 

 expected in a treatise bearing the name of so well-known 

 an authority as Mr. Merrill, the book is replete with 

 valuable information both to the geologist and the 

 architect. 



Mr. Merrill gives, in the introduction to his work, an 

 interesting sketch of the gradual substitution of stone for 

 wood as a building material among the early settlers in 

 New England, and then proceeds to sketch the distribu- 

 tion of the different varieties of building stones in the 

 several States and Territories of the Union. The chapters 

 which follow, on the minerals of building stones, and on 

 the physical and chemical characters of the rocks which 

 are employed in construction, are very admirably written ; 

 the illustrations of the microscopical structure of building 

 stones, and the remarks on the nature and causes of dis- 

 integration in different varieties, being alike excellent. 



In classifying building materials, Mr. Merrill very wisely 

 adopts a combination of practical and scientific methods. 

 Among the crystalline and vitreous rocks, he distinguishes, 

 in the first place, those which are simple or made up of 

 one mineral only — namely, steatite and soapstone, serpen- 

 tine (including the verdantique marbles), gypsum (in- 

 ■cluding alabaster and satin spar), and limestones with 

 dolomites. In dealing with the compound rocks, or those 

 built up of several different minerals, Mr. Merrill adopts 

 the usual petrographical distinction of massive and 

 schistose (or foliated) rocks. The former he divides into 

 the four groups of rocks containing free quartz, rocks 

 without quartz, but containing orthoclase felspar, rocks 

 with plagioclase felspar, and rocks without felspar. 

 The fragmental rocks are divided into the psammites 

 (sandstones, &c.), the pelites (clays, &c.), the volcanic 

 tuffs, and the rocks built up by organisms. 



The chapters on the methods of quarrying, working, 

 and testing building stones are especially admirable, and 

 the illustrations of the great quarries of the United States, 

 reproduced from photographs, are of great interest. The 

 remarks on the processes which have been devised for 

 the protection and preservation of building stones, and 

 the tables giving the crushing strength, specific gravity, 

 ratio of absorption, and chemical composition of all the 

 chief varieties of building stone employed in the United 

 States, cannot fail to be of great value to practical men. 

 It would be hard to find a more admirable example of 

 the value of exact scientific knowledge when applied to 

 the treatment of economic questions than is afforded by 

 the work before us. 



Les Champignons. Par A. Acloque. (Paris : J. B. Bail- 



lifere et Fils, 1892.) 

 The author of this book has found much to interest him in 

 the study of his subject, and he communicates in a clear, 

 pleasant style the leading facts and laws which have been 

 brought to light by mycologists. Having presented in 

 an introductory chapter some general considerations, 

 he proceeds to deal with the subject from the ana- 

 tomical, the physiological, and the economical points 

 of view. Finally he gives a summary of mycological 

 taxonomy. The book belongs to the " Bibliotheque 

 Scientifique Contemporaine," and is in every way worthy 

 of a place among the other volumes of the series. 



NO. I 158, VOL. 45] 



Theory of Heat. By J. Clerk Maxwell. Tenth Edition. 

 With Corrections and Additions by Lord Rayleigh. 

 (London : Longmans, Green, and Co., 1891.) 

 This book is so well known, and has been of such good 

 service to students, that it is scarcely necessary to do 

 more than note the fact that a tenth edition of it has 

 been issued. Only such corrections and additions have 

 been introduced as seemed, in Lord Rayleigh's judg- 

 ment, to be really called for. They are in great measure 

 derived from Clerk Maxwell's later writings. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of 'Na.tv'b.^. 

 No notice is taken of anonymous communications. ] 



The Implications of Science. 



Permit me, through your columns, to thank Mr. E. T. Dixon 

 for his letter, which appeared in Nature of December 10, 

 1891, p. 125, concerning my lecture on the implications of 

 science, and, very briefly, to reply to it. 



He is very much mistaken in thinking that I place our know- 

 ledge of "the law of contradiction" and of "our own con- 

 tinuous existence" in the same category. I regard them as 

 truths fundamentally distinct. The former is an abstract 

 principle, the latter a particular fact. Since Mr. Dixon merely 

 affirms without arguing, he must permit me to contradict him, 

 and say that the law of contradiction is a necessary and objective 

 truth — one that does not merely express a " verbal convention," 

 and is «^^ "of the nature of a definition." It is so objective 

 that Ofnnipotence itself could not violate it— could not, e.g., 

 cause a creature to have at the same time both four and only 

 three legs. But "our continuous existence" is so far from 

 being a necessary truth that, if an Omnipotent Creator exists, 

 there can be no impossibility in our annihilation. That we can- 

 not be annihilated while we know we are actually existing is, of 

 course, true ; but that fact, so far from serving Mr. bixon's 

 argument, is but an example of the validity of the law of contra- 

 diction. We cannot at the same time be both "consciously 

 existing" and "absolutely annihilated." My critic seems to be 

 still in bondage to that subjectivism and nominalism wherein I 

 was so long involved, and whence I only extricated myself 

 slowly and with much trouble. 



As to memory, I said that we may, as everybody knows, 

 make mistakes, but that nevertheless we are as certain concern- 

 ing some parts of the past as of the present. Most assuredly I 

 am quite as certain that I read Mr. Dixon's letter as that I am 

 now in the act of replying to it. Our confidence in our memory 

 cannot depend upon induction, because, if we had it not at 

 starting, we could make no induction or enumeration whatever. 



My "implications of science" are truths, and not "purely 

 verbal assertions," but I never affirmed any "peculiar certainty " 

 for "mathematical conclusions." Helmholtz has never shown, 

 to my knowledge, that two straight lines could ever inclose a space. 

 Of course, if his supposed "dwellers on a sphere" chose, as 

 Mr. Dixon says, to apply that term to what are not straight 

 lines, different conclusions would follow. No one denies that 

 two curved lines can be conceived of as inclosing a space. 



Similarly, if Mr. Dixon's inhabitants of the Dog Star chose, as 

 he again says, "to define four as i -h i -4- i," then for them 

 two and two would not be four. But who was ever so absurd 

 as to suppose they would be ? If any persons choose to give to 

 the term " an angle" the signification we express by the words 

 " a mutton chop," then certainly our conception of a triangle 

 would not apply ; for three such angles would not be equal to 

 two right angles. 



Mr. Dixon is good enough to instruct us that " the law of con- 

 tradiction never tells us whether anything is or is not." But 

 what man out of Bedlam would suppose that a statement of an 

 abstract general law would inform us about a particular concrete 

 thing ? On the other hand, the law of contradiction does not 

 tell us, and never by any possibility could tell us, " that the terms 

 ' is ' and ' is not ' are not applicable to the same thing " — though 



