June 27, 1872] 



NATURE 



^1Z 



change, the a:linic rays beinjj altogether the most effective.* 

 Mr. E. Biidde has recently described a remarkable experiment in 

 this direction. He found that a dilTerential theimometer tilled 

 with chlorine expanded about seven times more in the violet 

 than in the red ray of the soUr spectrum ; when the same 

 thermometer wa^ lillei with CO., no aclion was noticed, t 



As the combination of hydrogen and chlorine is effected 

 without change of volume, it is obvious tliat the molecule cl does 

 not unite with the molecule ed, forming a compound molecule 

 cl-cd. The conclusion is thereore unavoidable that ejch mole- 

 cule has been divided into two equal parts, and that by affinity, 

 like parts have been separated, and unhke parts have been united. 

 These parts are the smallest quantities that cin be isolated, and 

 are in fact the atoms recognised by the chemist. If this smallest 

 combining proportion or atom be designated by a, the actual 

 composition ot t'a; hydrogen molecule d, weighing 2, may be 

 clearly represented by al-al (weight i + I ), and the chlorine 

 molecule <•./ weighing 72, by <z,/i?/ (weight 35"5 + 35'5). As 

 the attraction ol al to al, and of ad to nd is, after exposure to 

 light, less than of <?/ to tii, there is an instantaneous chemical 

 change by which one molecule of hydrogen and one molecule of 

 chlorine are transformed into two molecules of hydrochloric 

 acid gas. This reaction is clearly indicated by the following 

 equation : al-al + ad-ad — alad + alad = 2 alad. 



The symbols here used are intended to convey to the mind an 

 idea of the relative size of combining parts, which is not sj 

 apparent when expressed as follows : — 



H,, + Cl, = HCl + HC1= 2HCI. 



From the simplest of molecular types we might proceed to the 

 most complex ; and, throughout, if we consider the combining 

 proportion of each simple constituent as either a unit or a mul- 

 tiple of a unit, the composition of each molecule may be ex- 

 pressed by whole numbers. Thus having as many different 

 kinds of units as there are elements, any true chemical combina- 

 tion may be symbolised by a combination of arithmetical ratios. 

 This method, under the light of the atomic theory, clearly reveals 

 the harmonic relations of molecular constituents, which, seen 

 from the stand-point of percentage composition, appear uncon- 

 nected and discordant. 



It must be admitted that many of the reactions of well-known 

 bodies have not yet been determined quantitatively ; yet were 

 they made out, we should not be able to demonstrate by experi- 

 ment the truth of the atomic doctrine. It still remains a theory, 

 in favour of which there are many facts and phenomena that 

 collectively form an argument not easily to be outweighed. 

 This evidence may be brietly summarised as follows : — 



1. Aloinic U'iiihts. Elements combine in extremely minute 

 parts, according fo the law of definite and multiple proportions. 

 The atomic weight of an element is either its equivalent weight or 

 a multiple of i', as such multiple cannot be divided by reactions, 

 its weight must conform with the atomic number. Whatever 

 changes of position the combining weight of an element may 

 undergo in a series of molecular metamorphoses, that is to say, 

 however many times it may be displaced and replaced in chemical 

 combinations, it invariably retains its characteristic weight. 

 This invariability of weight is an essential property of the atom. 



2. Atomic Volume. Gases unite in equal volumes or multiple 

 volumes. If hydrogen be taken as unity, the density of each 

 elementary gas is identical with the weight of its atom. The 

 atomic volume, determined by dividing the atomic weight of a 

 body by its specific gravity, has been the means of revealing 

 many interesting relations among compounds of similar structure, 

 and among many containing different components and of unlike 

 structure. 



3. Atomic Ileal. It has been shown by experiment that quan- 

 tities of each element conforming with its atomic number have 

 the same capacity for heat, excepting only carbon, boron, and 

 silicon ; these, it is believed, will yet be found to conform to the 

 law, that the specific heats of atoms are the same. This law is 

 regarded as a direct confirmation of atomic weights. 



4. Molecules. According to ihe atomic theory chemical forces 

 are brought in equilibrium when atoms combine and form a 

 molecule. Every gas and every vapour undecomposed has a 

 density proportional to its molecular weight. All known mole- 

 cular combin.ations and combining proportions are in accordance 

 with the atomic doctrine. Decomposition by electrolysis affords 



• A Treatise on the Forces which produce the Organisation of Plants. By 

 John William Draper. (New York : Harper and Brothers, 1843.) 

 t Pogg. Annatcn for 1871, No. lo. 



some evidence that the constituent parts of a molecule which arc 

 simultaneously separated are pro[)ortionate to atomic weights. 



5. Atomic coiiiliiniiio capacity. Tne modern doctrine of types 

 and substitutions is solely based on the individuality of the atom, 

 without which the whole fabric of typical structures must fall. 



6. Isomerism. The fact that bodies containing the same 

 elements, and in precisely the same proportions, exhibit different 

 properties, has been thus far accounted for, only on the supposi- 

 tion that atoms are differently arrangeil in each body. These 

 differences in arrangement depend not only on the relative posi- 

 tion of atoms, but also on the order as to time in whic'i they 

 combin'i ; for two or more atoms having such precedence over 

 others as to combine first, may, by that means, form a radical of 

 such permanence as to play the part of an ai om. Apart from the 

 question of radicals, we may ascertain the number of different 

 bodies which can be formed from the same number of dilfereut 

 atoms, by an applicatioa of the mathematical law of permuta- 

 tions. 



7. Homogeneity. The uniformity of structure and appearance 

 of any element or chemical combination of elements furnishes 

 the most palpab'e proof of the identity in size and shape of those 

 definite parts which we designate as molecules. This homo- 

 geneity IS retained under different tlegrees of pressure, thus 

 making it apparent that molecules are not identical in structure, 

 but that they approach and recede in precisely the same manner 

 under the same conditions. 



Finally. — The foregoing statement regarding the existence 01 

 atoms which are indivisible and indestructible under the present 

 order of things does not preclude the supposition that the atom 

 may be a cluster of smaller particles held together by a power- 

 ful affinity, which, when counteracted, would leave them free 

 to move within a given sphere. On this assumption it is highly 

 probable that the rehttive position of such particles may modify 

 the combining capacity of the atom. IVIoreover, the normal 

 motion of such particles may determine not only the peculiari- 

 ties of elemental spectra, but produce other effects not dependent 

 on the amplitude of atomic oscillations, thus favourino- the in- 

 ference that the atom itself is a receptacle of force. 



Samuel D. Tillman 



BLOOD-RELATIONSHIP '■ 



T PROPOSE in this memoir to deduce by fair reasoning 

 from acknowledged facts a more definite notion than now 

 exists of the meaning of the word "kinship." It is my aim 

 to analyse anl describe the complicated connection th.at 

 binds an individual, hereditarily, to his parents and to his 

 brothers and sisters, and, therefore, by an extension ol similar 

 links, to his more distant kinsfolk. I hope by these means to 

 set forth the doctrines of heredity in a more orderly and explicit 

 manner than is otherwise practicable. 



From the well-known circumstance that an individual may 

 transmit to his descendants ancestral qualities which he does not 

 himself possess, we arc assured that they could not have been 

 altogether destroyed in him, but must have maintained their 

 existence in a latent form. Therefore each individual may pro- 

 perly be conceived as consisting of two parts, one of which is 

 latent and only known to us by its effects on his posterity, while 

 the other is paten: and constitutes the person manifest to our 

 senses. 



The adjacent, and, in a broad sense, separate lines of growth 

 in which the patent and latent elements are situated, diverge from 

 a common group and converge to a common contribution, be- 

 cause they were both evolved out of elements contained in a 

 structureless ovum, and they jointly contribute the elements 

 which form the structureless ova of tneir offspring. 



The annexed diagram illustrates my meaning, and serves to 

 show clearly that the span of each of the links in the general 

 chain of heredity extends from one structureless stage to another, 

 and not from person to person. 



Struc'urelcss ( Adult Father 1 Structureless 



elements in .j ', elements in 



Father ( Latent in Father ) offspring. 



I will now proceed to consider the quality of the several rela- 

 tionships by which the above terms are connected together. 



The observed lacts of Reversion enable us to prove that the 

 latent elements must be greatly more varied than those that are 

 personal or patent. The arguments are as follows : — (i) There 



• Read before the Royal Society, June 13, by Francis Gallon, F.R.S, 



