6 REPORT 1870. 



an experienced smoker sends out a dexterous pufF of smoke into the still air, but a 

 more evanescent phenomenon it is diiEcult to conceive. This evanescence is owing 

 to the viscosity of the air ; but Helmholtz has shown that in a perfect fluid such 

 a whirling ring, if once generated, would go on whirling for ever, would always con- 

 sist of the very same portion of the fluid which was first set whirling, and could never 

 be cut in two by any natural cause. The generation of a ring-vortex is of course 

 equally beyond the power of natural causes, but once generated, it has the pro- 

 perties of individuality, permanence in quantity, and indestructibility. It is also 

 the recipient of impulse and of energy, which is all we can aflirm of matter ; and 

 these ring-vortices are capable of such varied connexions and knotted self-involu- 

 tions, that the properties of differently knotted vortices must be as different as those 

 of different kinds of molecules can be. 



If a theory of this kind shoidd be found, after conquering the enormous mathe- 

 matical difficulties of the subject, to represent in any d gree the actual properties 

 of molecules, it will stand in a very different scientific position from those theories 

 of molecular action which are formed by investing the molecule with an arbitrary 

 system of central forces invented expressly to account for the observed phenomena. 



In the vortex theory we have nothing arbitrary, no central forces or occult pro- 

 perties of any other kind. We have nothing but matter and motion, and when the 

 vortex is once started its properties are all determined from the original impetus, 

 and no fiu-ther assumptions are possible. 



Even in the present undeveloped state of the theory, the contemplation of the 

 individuality and indestructibility of a ring-vortex in a perfect fluid cannot fail 

 to disturb the commonly received opinion that a molecule, in order to be permanent, 

 must be a very hard body. 



In fact one of the first conditions which a molecule must fulfil is, apparently, 

 inconsistent with its being a single hard body. We know from those spectroscopic 

 researches which have thrown so much light on different branches of science, that 

 a molecule can be set into a state of internal vibration, in which it gives off to the 

 smTouuding medium light of definite refrangibility — light, that is, of definite wave- 

 length and definite period of vibration. The fact that all the molecules (say, of 

 hydrogen) which we can procure for om* experiments, when agitated by heat or by 

 the passage of an electric spark, vibrate precisely in the same periodic time, or, to 

 speak more accurately, that their vibrations are composed of a system of simple 

 vibrations having always the same periods, is a very remarkable fact. 



I must leave it to others to describe the progress of that splendid series of 

 spectroscopic discoveries by which the chemistry of the heavenly bodies has been 

 brought ^vithiu the range of human inquiry. I wish rather to direct yom' attention 

 to the fact that, not only has every molecido of terrestrial hydrogen the same 

 system of periods of free vibration, but that the spectroscopic exammation of the 

 light of the sun and stars shows that, in regions the distance of which we can only 

 feebly imagine, there are molecules vibrating in as exact unison with the molecules 

 of terrestrial hydrogen as two tuning-forks tuned to concert pitch, or two watches 

 regulated to solar time. 



Now this absolute equality in the magnitude of quantities, occurring in all parts 

 of the universe, is worth our consideration. 



The dimensions of individual natm-al bodies are either quite indetenninate, as in 

 the case of planets, stones, trees, &c., or they vary within moderate limits, as 

 in the case of seeds, eggs, &c. ; but even in these cases small quantitative differ- 

 ences are met with which do not interfere with the essential properties of the body. 



Even crystals, which are so definite in geometrical form, are variable with respect 

 to their absolute dimensions. 



Among the works of man we sometimes find a certain degree of uniformity. 



There is a imiformity among the different bullets which are cast in the same 

 mould, and the different copies of a book printed from the same type. 



If we examine the coins, or the weights and measures, of a civilized country, we 

 find a uniformity, which is produced by careful adjustment to standards made and 

 provided by the state. The degree of uniformity of these national standards is a 

 measm-e of that spirit of justice in the nation which has enacted laws to regulate 

 them and appointed oflicera to test them. 



