666 heport— 1884. 



examination of a spectrum by Lockyer's method, to predict the changes which it 

 will undergo, either on alteration of temperature, or by an increase or decrease of 

 quantity. There appears to be no theoretical difficulty in assuming that the relative 

 intensity of the lines may vary when the temperature is altered, and the molecular 

 theory of gases furnishes us with a plausible explanation of the corresponding 

 change when the relative quantities of the luminous elements in a mixture are 

 altered. Lockyer has proposed a different explanation of the facts. According to 

 him, every change of relative intensity means a corresponding change of molecular 

 complexity, and the lines which we see strong near the poles, would bear the same 

 relation to those which are visible throughout the field, as a line spectrum bears to 

 a band spectrum ; but then almost every line must be due to a different molecular 

 grouping, a conclusion which is scarcely capable of being upheld without very 

 cogent proof. 



The examination of the absorption spectra of salts, saline and organic liquids, 

 first by Gladstone, and afterwards by Bunsen, and by Russell, as well as by Hartley 

 for the ultra-violet, and by Abney and Festing for the infra-red region, have led to 

 interesting residts in relation to molecular chemistry. Thus Hartley finds that in 

 some of the more complicated aromatic compounds, definite absorption bands in the 

 more refrangible region are only produced by substances in which three pairs of 

 carbon atoms are doubly linked, as in the benzene ring, and thus the means of 

 ascertaining this double linkage is given. The most remarkable results obtained 

 by Abney and Festing show that the radical of an organic body is always repre- 

 sented by certain well-marked absorption bands, differing, however, in position, 

 according as it is linked with hydrogen, a halogen, or with carbon, oxygen, or 

 nitrogen. Indeed, these experimenters go so far as to say that it is highly pro- 

 bable that by this delicate mode of analysis the hypothetical position of any hydro- 

 gen which is replaced may be identified, thus pointing out a method of physical 

 orientation of which, if confirmed by other observers, chemists will not be slow 

 to avail themselves. This result, it is interesting to learn, has been rendered more 

 than probable by the recent important researches of Perkin on the connection 

 between the constitution and the optical properties of chemical compounds. 



One of the noteworthy features of chemical progress is the interest taken by 

 physicists in fundamental questions of our science. We all remember, in the first 

 place, Sir William Thomson's interesting speculations, founded upon physical phe- 

 nomena, respecting the probable size of the atom, viz., ' that if a drop of water 

 were magnified to the size of the earth, the constituent atoms would be larger than 

 small shot, but smaller than cricket balls.' Again, Helmholtz in the Faraday 

 lecture, delivered in 1881, discusses the relation of electricity and chemical energy, 

 and points out that Faraday's law of electrolysis, and the modern theory of valency, 

 are both expressions of the fact, that when the same quantity of electricity passes 

 through an electrolyte, it always either sets free, or transfers to other combina- 

 tions, the same number of units of affinity at both electrodes. Helmholtz further 

 argues, that if we accept the Daltonian atomic hypothesis, we cannot avoid the 

 conclusion that electricity, both positive and negative, is divided into elementary 

 portions which behave like atoms of electricity. He also shows that these charges 

 of atomic electricity are enormously large as compared, for example, with the 

 attraction of gravitation between the same atoms ; in the case" of oxygen and 

 hydrogen, 71,000 billion times larger. 



A further subject of interest to chemists is the theory of the vortex-ring con- 

 stitution of matter thrown out by Sir William Thomson, and lately worked out 

 from a chemical point of view by J. J. Thomson, of Cambridge. He finds that 

 if one such ring be supposed to constitute the most simple form of matter, say the 

 monad hydrogen atom, then two such rings must, on coming into contact with 

 nearly the same velocity, remain enchained together, constituting what we know as 

 the molecule of free hydrogen. So, in like manner, systems containing two, three, 

 and four such rings constitute the dyad, triad, and tetrad atoms. How far this 

 mathematical expression of chemical theory may prove consistent with fact remains 

 to be seen. 



Another branch of our science which has recently attracted much experimental 



