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SCIENCE. 



LN. S. Vol. XVIII. No. 460. 



fundamental support of experimental 

 knowledge was lacking. 



In 1775, Dr. Bryan Higgins, of London, 

 published the prospectus of a course of lec- 

 tures upon chemistiy, in which the atomic 

 hypothesis was strongly emphasized. It 

 was still, however, only an hypothesis, 

 quite as ineffectual as Swedenborg's at- 

 tempt, and it led to nothing. Dr. Higgins 

 recognized seven elements ; earth, water, 

 alkali, acid, air, phlogiston and light; each 

 one consisting of 'atoms homogeneal, ' 

 these being 'impenetrable, immutable in 

 figure, inconvertible,' and all 'globular, or 

 nearly so.' He speculated upon the at- 

 tractions and repulsions between these 

 bodies, but he seems to have solved no prob- 

 lem and to have suggested no research. 

 William Higgins, on the other hand, whose 

 work appeared in 1789, showed more in- 

 sight into the requirements of true science, 

 and had some notions concerning definite 

 and multiple proportions. . His concep- 

 tion of atomic union to form molecules was 

 fairly clear, but the distinct statement of a 

 quantitative law was just beyond his reach. 

 In 1814, however, when Dalton's discov- 

 eries were widely known and accepted, 

 Higgins published a reclamation of 

 priority.* In this, with much bitterness, 

 he claims to have completely anticipated 

 Dalton, a claim which no modern reader 

 has been able to allow. In Robert Angus 

 Smith's 'Memoir of John Dalton and His- 

 tory of the Atomic Theory, 'f the work of 

 Bryan and William Higgins is quite thor- 

 oughly discussed, and, therefore, we need 

 not consider the matter any more fully 

 now. We see that atomic theories were 

 receiving the attention of chemists long 



* ' Experiments and Observations on the Atomic 

 Tlieory and Electrical Phenomena.' By William 

 Higgins, Esq., etc., Dublin, 1814. 



t Memoirs of the Literary and Philosophical 

 Society of Manchester, Second Series, Volume 13, 

 18.56. 



before Dalton's time, although none of 

 them went much beyond the speculative 

 stage, or was given serviceable form. They 

 were dim f oreshadowings of science ; noth- 

 ing more. 



In order that a new thought shall be 

 acceptable, certain prerequisite conditions 

 must be fulfilled. If the ground is not pre- 

 pared, the seed can not be fruitful ; if men 

 are not ready, no harvest will be reaped. 

 Only when the time is ripe, only when long 

 lines of evidence have begun to converge, 

 can a new tlieory command attention. 

 Dalton's opportunity came at the right 

 moment, and he knew how to use it well. 

 Elements had been defined; the constancy 

 of matter was established ; pneumatic chem- 

 istry was well developed, and great niun- 

 bers of quantitative analyses awaited in- 

 terpretation. The foundations were ready 

 for the master builder, and Dalton was 

 the man. His theory could at once be 

 tested by the accumulated data, and when 

 that had been done it was found to be 

 worthy of acceptance. 



It is not my purpose to discuss in detail 

 the processes of Dalton 's mind. The story 

 is told in his own note-books, which have 

 been given to the public by Roscoe and 

 Harden,* and it has been sufficiently dis- 

 cussed by others. We now know that 

 Dalton was thoroughly imbued with the 

 corpuscular ideas of Newton, and that, 

 when studying the diffusion of gases, he 

 was led to the belief that the atoms of 

 different substances must be different in 

 size. Upon applying this hypothesis to 

 chemical problems, he discovered that these 

 diffei'ences were in one sense measurable, 

 and that to every element a single, definite, 



* ' A New View of the Origin of Dalton's Atomic 

 Theory,' etc. By Sir Henry E. Roscoe and Arthur 

 Harden. London, 1896. 



See also Debus, in Zeits. Physikal. Chein., Bd. 

 20, p. 359, and a rejoinder by Roscoe and Harden 

 in Bd. 22, p. 241. 



