Chapter XXIX: Introduction (5)

There is another property of many organic substances which is called the _Law of Substitution_. The {364} Hydrogen of the organic substance may often be replaced by Chlorine, Bromine, Iodine, or some other elements, without the destruction of the primitive type or constitution of the compound so modified. And this substitution may take place by several successive steps, giving rise to a series of substitution-compounds, which depart more and more in properties from the original substance. This Law also gives rise to a special notation. Thus a certain compound called _Dutch liquid_ has the elements _C__4 _H__4 _Cl__2: but this substance is affected by chlorine (_Cl_) in obedience to the law of substitution; one and two equivalents of hydrogen being successively removed by the prolonged action of chlorine gas aided by sunshine. The successive products may be thus written _H__3 _H__2 _C__4 _H__4 _Cl__2; _C__4 { } _Cl__2; _C_4 { } _Cl__2. _Cl_ _Cl_2

Perhaps at a future period, chemical symbols, and especially those of organic bodies, may be made more systematic and more significant than they at present are.

APHORISM XXVII.

_In using algebraical symbols as a part of scientific language, violations of algebraical analogy are to be avoided, but may be admitted when necessary._

AS we must in scientific language conform to etymology, so must we to algebra; and as we are not to make ourselves the slaves of the former, so also, not to the latter. Hence we reject such crystallographical notation as that of Mohs; and in chemistry we use _C__2, _O__3 rather than _C_², _O_³, which signify the square of _C_ and the cube of _O_. But we may use, as we have said, both the comma and the sign of addition, for chemical combination, for the sake of brevity, though both steps of combination are really addition. {365}

APHORISM XXVIII.

_In a complex science, which is in a state of transition, capricious and detached derivations of terms are common; but are not satisfactory._

IN this remark I have especial reference to Chemistry; in which the discoveries made, especially in organic chemistry, and the difficulty of reducing them to a system, have broken up in several instances the old nomenclature, without its being possible at present to construct a new set of terms systematically connected. Hence it has come to pass that chemists have constructed words in a capricious and detached way: as by taking fragments of words, and the like. I shall give some examples of such derivations, and also of some attempts which have more of a systematic character.

I have mentioned (Aph. **XX. sect. 7) the word _Ellagic_ (acid), made by inverting the word _Galle_. Several words have recently been formed by chemists by taking syllables from two or more different words. Thus Chevreul discovered a substance to which he gave the name **_Ethal_, from the first syllables of the words _ether_ and _alcohol_, because of its analogy to those liquids in point of composition[73\4]. So Liebig has the word _chloral_[74\4].

[Note: 73\4: Turner's _Chemistry_, 1834, p. 955]

[Note: 74\4: Berzelius' _Jahresbericht_, xv. p. 372.]

Liebig, examining the product of distillation of alcohol, sulphuric acid and amber, found a substance which he termed _Aldehyd_, from the words _Al_cohol _dehyd_rogenated[75\4]. This mode of making Words has been strongly objected to by Mr. Dumas[76\4]. Still more has he objected to the word _Mercaptan_ (of Zeise), which {366} he says rests upon a mere play of words; for it means both _mercurium captans_ and _mercurio aptum_.

[Note 75\4: _Ibid._ xvi. p. 308.]

[Note 76\4: _Leçons de Chimie_, p. 354.]

Dumas and Peligot, working on pyroligneous acids, found reason to believe the existence of a substance[77\4] which they called _methylene_, deriving the name from _methy_, a spirituous fluid, and _hyle_, wood. Berzelius remarks that the name should rather be _methyl_, and that ὕλη may be taken in its signification of matter, to imply the Radical of Wine: and he proposes that the older Æther-Radical, _C__4 _H__10 shall be called _Æthyl_, the newer, _C__2 _H__6, _Methyl_.

[Note 77\4: Berzelius' _Jahresbericht_, xv. (1836).]

This notion of marking by the termination _yl_ the hypothetical compound radical of a series of chemical compounds has been generally adopted; and, as we see from the above reference, it must be regarded as representing the Greek word ὕλη: and such hypothetical radicals of bases have been termed in general _basyls_.

Bunsen obtained from Cadet's fuming liquid a substance which he called _Alkarsin_ (_alk_ali-_ars_enic?): and the substance produced from this by oxidation he called _Alkargen_[78\4]. Berzelius was of opinion, that the true view of its composition was that it contained a compound ternary radical = _C_^6 _H_^12 _As_^2, after the manner of organic bodies; and he proposed for this the name[79\4] _Kakodyl_. Alkarsin is Kakodyl-oxyd, [.]Kd, Alkargen is Kakodyl-acid, [∴]Kd.

[Note 78\4: _Ibid._ xviii. p. 497.]

[Note 79\4: _Ibid._ xx. p. 527.]

The discovery of Kakodyl was the first instance of the insulation of an organic metallic _basyl_[80\4].

[Note 80\4: Miller's _Chemistry_, iii. 220.]

The first of the Hydrocarbon Radicals of the Alcohols was the radical of Tetrylic alcohol obtained by Kolbe from Valerate of Potash, and hence called _Valyl_ _C__16 _H__18.

_Chloroform_ is per_chloride_ of _formyl_, the hypothetical radical of formic acid[81\4].

[Note 81\4: Dumas, _Leçons sur la Phil. Chim._ p. 356.]

{367} The discovery of such bases goes back to 1815. The substance formerly called _Prussiate of Mercury_, being treated in a particular manner, was resolved into metallic mercury and _Cyanogen_. This substance, _Cyanogen_, is, according to the older nomenclature, _Bicarburet of Nitrogen_; but chemists are agreed that its most convenient name is _Cyanogen_, proposed by its discoverer, Gay-Lussac, in 1815[82\4]. The importance of the discovery consists in this; that this substance was the first compound body which was distinctly proved to enter into combination with elementary substances in a manner similar to that in which they combine with each other.

[Note 82\4: Turner's _Chemistry_ (1834), p. 420. Miller's _Chemistry_, ii. 66.]

The truth of our Aphorism (XXV.) that in such a science as chemistry, the history of the scientific nomenclature is the history of the science, appears from this; that the controversies with respect to chemical theories and their application take the form of objections to the common systematic names and proposals of new names instead. Thus a certain compound of potassa, sulphur, hydrogen, and oxygen, may be regarded either as _Hydrosulphate of Potassa_, or as _Sulphide of Potassium in solution_, according to different views[83\4]. In some cases indeed, changes are made merely for the sake of clearness. Instead of _Hydrochloric_ and _Hydrocyanic_ acid, many French writers, following Thenard, transpose the elements of these terms; they speak of _Chlorhydric_ and _Cyanhydric_ acid; by this means they avoid any ambiguity which might arise from the use of the prefix _Hydro_, which has sometimes been applied to compounds which contain water[84\4].

[Note 83\4: Miller's _Chemistry_, vol. ii. p. 583.]

[Note 84\4: _Ibid._ ii. 433.]

An incompleteness in chemical nomenclature was further felt, when it appeared, from the properties of various substances, that mere identity in chemical composition is not sufficient to produce identity of chemical character or properties[85\4]. The doctrine of {368} the existence of compounds identical in ultimate composition, but different in chemical properties, was termed _Isomerism_. Thus chemists enumerate the following compounds, all of which contain carbon and hydrogen in the proportion of single equivalents of each[86\4];--_Methylene_, _Olefiant gas_, _Propylene_, _Oil gas_, _Amylene_, _Caproylene_, _Naphthene_, _Eleene_, _Peramylene_, _Cetylene_, _Cerotylene_, _Melissine_.

[Note 85\4: _Ibid._ ii. 653.]

[Note 86\4: Miller's _Chemistry_, ii. p. 654.]

I will, in the last place, propound an Aphorism which has already offered itself in considering the history of Chemistry[87\4] as having a special bearing upon that Science, but which may be regarded as the supreme and ultimate rule with regard to the language of Science.

[Note 87\4: _Hist. Ind. Sc._ b. xiv. c. 1.]

APHORISM XXIX.

_In learning the meaning of Scientific Terms, the history of science is our Dictionary: the steps of scientific induction are our Definitions._

IT is usual for unscientific readers to complain that the technical terms which they meet with in books of science are not accompanied by plain definitions such as they can understand. But such definitions cannot be given. For definitions must consist of words; and, in the case of scientific terms, must consist of words which require again to be defined: and so on, without limit. _Elementary substances_ in chemistry, for instance, what are they? The substances into which bodies can be _analysed_, and by the junction of which they are _composed_. But what is _analysis_? what is _composition_? We have seen that it required long and laborious courses of experiment to answer these questions; and that finally the balance decided among rival answers. And so it is in other cases. In entering upon each science, we come upon a new set of words. And how are we to learn {369} the meaning of this collection of words? In what other language shall it be explained? In what terms shall we define these new expressions? To this we are compelled to reply, that we cannot translate these terms into any ordinary or familiar language. Here, as in all other branches of knowledge, the meaning of words is to be sought in the progress of thought. It is only by going back through the successful researches of men respecting the _composition_ and _elements_ of bodies, that we can learn in what sense such terms can be understood, so as to convey real knowledge. In order that they may have a meaning for us, we must inquire what meaning they had in the minds of the authors of our discoveries. And the same is the case in other subjects. To take the instance of Morphology. When the beginner is told that every group of animals may be reduced to an _Archetype_, he will seek for a definition of Archetype. Such a definition has been offered, to this effect: the Archetype of a group of animals is a diagram embodying all the organs and parts which are found in the group in such a relative position as they would have had if none had attained an excessive development. But, then, we are led further to ask, How are we in each case to become acquainted with the diagram; to know of what parts it consists, and how they are related; and further; What is the standard of _excess_? It is by a wide examination of particular species, and by several successive generalizations of observed facts, that we are led to a diagram of an animal form of a certain kind, (for example, a vertebrate;) and of the various ways, excessive and defective, in which the parts may be developed.

This craving for definitions, as we have already said, arises in a great degree from the acquaintance with geometry which most persons acquire at an early age. The definitions of geometry are easily intelligible by a beginner, because the idea of space, of which they are modifications, is clearly possessed without any special culture. But this is not and cannot be the case in other sciences founded upon a wide and exact observation of facts. {370}

It was formerly said that there was no Royal Road to Geometry: in modern times we have occasion often to repeat that there is no Popular Road--no road easy, pleasant, offering no difficulty and demanding no toil,--to Comparative Anatomy, Chemistry or any other of the Inductive Sciences.

THE END.

CAMBRIDGE: PRINTED BY C. J. CLAY, M.A. AT THE UNIVERSITY PRESS.

Transcriber's Notes

Whewell published the first edition of the _Philosophy of the Inductive Sciences_ in 1840 in two volumes, as a companion to the 1837 _History of the Inductive Sciences_. Revised second editions of both works appeared in 1847. The third editions saw a major reshaping of the _Philosophy_: a two volume _History of Scientific Ideas_ (1858; in Project Gutenberg as #69093), _Novum Organon Renovatum_ (1858; the present text, relying upon resources kindly provided by the Internet Archive), and _On the Philosophy of Discovery: chapters historical and critical_ (1860; long since in Project Gutenberg's collection as #5155). (The third edition of the _History of the Inductive Sciences_ is available in PG as #68693.)

Adaptations in this text

In the present text footnotes are numbered by Book and are placed after the paragraph to which they attach; in the original, notes were numbered by chapter. Page numbers appear in { }, or {{ }} when the number is not printed. Where a word was hyphenated across pages the number has been placed before the word. Fractions have been transcribed as numerator ⁄ denominator; the original usually has numerator over a line with denominator below.

Some unusual symbols occur. On pages 357 and 358, there are italic letters with a number written above them. On two occasions B has a 1 above it, and once C has ½ above it. On page 364 a formula is written with two entries containing H on a line above Cl. These superpositions have been preserved at the cost of some short lines. The other oddities have been captured by using [ ] to indicate items above the following character. (They should not be confused with the use of [ ] for footnote anchors.) For superscripts ^ has been used except for expressions using only the superscripted numbers available in Unicode. Subscripts are indicated by a _ preceding the character. (This unfortunately results in double __ when the preceding characters are in italics.)

On pages 152 and 197 Whewell uses a raised dot as a decimal point and in footnote 26\3 a comma. These have been replaced by a mid dot.

Inductive Charts

At the end of Book II., Whewell included two very large inserts, described in some detail in the Book itself. They were not captured by the scans available in the Internet Archive. I was kindly provided with photographs of them. Those charts were four times as wide as the normal page and a quarter as long. In the html version they have been fairly accurately represented via tables; but with up to 25 columns these tables will be very difficult to decipher on small screens. In the text version, coded structure diagrams have been used, which again utilise the full 70 spaces Project Gutenberg allows. Rather than the tree shape Whewell used, the diagrams have been made to flow from left to right.

Corrections

Corrections are comparatively few. Apart from the silent ones, they have been marked by ** and are listed below.

Page Printed text Corrected text {{xiii}} v iii LXX. LXXIII. LXXXV. LXXXII. p. 12 of and p. 128 word work note 21\3 i. ii. p. 322 Wafferstoff Wasserstoff p. 365 XV. XX. Ethol Ethal

Given the various editions, some of the internal cross-references turn out to be obsolete or erroneous: note 11\3 reads B. viii. c. iii. but it refers actually to Book viii. c. ii. article 3 in earlier editions and in the _History of Scientific Ideas_, cf. Aphorism 88 in Book I. of the present volume. Compare also Aphorism 19 in this volume's Book IV. notes 58\3 and 59\3 refer to Book v. c. i. For the present third edition they should have been aimed at that chapter of the _History of Scientific Ideas_.

There are some inconsistencies, notably in spelling, which have in general not been adjusted; nor have Whewell's unbalanced quotation marks and positioning of footnote anchors been modernized.