8 EEPORT — 1887. 



something between a heap of small shot and a heap of cricket-balls. Or 

 again, to take Clifford's illustration, you know that our best microscopes 

 magnify from 6,000 to 8,000 times ; a microscope which would magnify 

 that result as much again would show the molecular structure of water. 

 Or again, to put it in another form, if we suppose that the minutest organ- 

 ism we can now see were provided with equally powerful microscopes, 

 these beings would be able to see the atoms. 



Next, as to the indivisibility of the atom, involving also the question 

 as to the relationships between the atomic weights and properties of the 

 several elementary bodies. 



Taking Dalton's aphorism, ' Thou knowst no man can split an atom,' 

 as expressing the view of the enunciator of the atomic theory, let us see 

 how far this idea is borne out by subsequent work. In the first place, 

 Thomas Thomson, the first exponent of Dalton's generalisation, was torn 

 by conflicting beliefs until he found peace in the hypothesis of Prout, that 

 the atomic weights of all the so-called elements are multiples of a com- 

 mon unit, which doctrine he sought to establish, as Thorpe remarks, by 

 some of the very worst quantitative determinations to be found in chemi- 

 cal literature, though here I may add that they were not so incorrect as 

 Dalton's original numbers. 



Coming down to a somewhat later date, Graham, whose life was devoted 

 to finding what the motion of an atom was, freed himself from the bond- 

 age of the Baltonian aphorism, and defined the atom not as a thing which 

 cannot be divided, but as one which has not been divided. With him, as 

 with Lucretius, as Angus Smith remarks, the original atom may be far 

 down. 



But speculative ideas respecting the constitution of matter have been 

 the scientific relaxation of many minds from olden time to the present. In 

 the mind of the early Greek the action of the atom as one substance 

 taking various forms by unlimited combinations was sufficient to account 

 for all the phenomena of the world. And Dalton himself, though up- 

 holding the indivisibility of his ultimate particles, says : ' We do not 

 know that any of the bodies denominated elementary are absolutely in- 

 decomposable.' Again Boyle, treating of the origin of form and quality, 

 says : ' There is one universal matter common to all bodies — an extended 

 divisible and impenetrable substance.' Then Graham in another place 

 expresses a similar thought when he writes : ' It is conceivable that 

 the various kinds of matter now recognised as different elementary sub- 

 stances may possess one and the same ultimate or atomic molecules exist- 

 ing in diflerent conditions of movement. The essential unity of matter 

 is an hypothesis in harmony with the equal action of gravity upon all 

 bodies.' 



What experimental evidence is now before us bearing upon these 

 interesting speculations ? In the first place, then, the space of fifty years 

 has completely changed the face of the inquiry. Not only has the number 

 of distinct well-established elementary bodies increased from fifty-three in 



