420 



SCIENCE 



[N. S. Vol. XLVI. No. 1192 



parison with the size of the atom than is 

 the sun when compared with the dimen- 

 sions of its planetary system. 



The special modification of Rutherford's 

 theory which has met with the most suc- 

 cess is that due to Bohr. The very re- 

 markable features of this theory have been 

 made the subject of Professor Millikan's 

 address, which has already been given, so 

 they need not be mentioned here. How- 

 ever, in spite of its success, Bohr's theory 

 possesses in common with the other special 

 views of atomic structure which have been 

 developed, the limitation that its applica- 

 tion has been restricted to one special class 

 of phenomena, those of radiation, and that 

 it is too simple to give a mechanism which 

 will act as any except the most simple of 

 atoms. In the Bohr atom the negative elec- 

 trons external to the nucleus are all sup- 

 posed to lie in the same plane with the nu- 

 cleus, while the structural relations of or- 

 ganic molecules seem to indicate that at 

 least the outer electrons do not lie in a 

 plane (except when only two in number) 

 but that they have a three-dimensional ar- 

 rangement. 



It was found by Moseley that if the ele- 

 ments are arranged in order according to 

 their X-ray spectra, they fall in the same 

 order as they do in the periodic system. If 

 arranged in this way, beginning with hy- 

 drogen as 1, and helium as 2, they are said 

 to be arranged according to their atomic 

 numbers. In our ordinary system of ele- 

 ments there are in all 91 elements from 

 helium to uranium inclusive, and in addi- 

 tion to these there is hydrogen which makes 

 92 in all. Of these 86 or 87 have been dis- 

 covered and 6 or 5 remain to be found. 

 It is the purpose of this paper to present 

 some relations which have been found by 

 the writer and his students, which have a 

 bearing on the structure of the atoms of 

 these elements, upon the problem of their 

 stability, and their formation by evolution. 



1. AEE THE EHEMENTS INTEA-ATOMIC COM- 

 POUNDS OF HYDROGEN? 



One of the first suggestions in regard to 

 the structure of the atom was made by 

 Prout in 1815, or a little over a century 

 ago. Prout found, on the basis of his own 

 experiments and the more accurate work 

 of Gay-Lussac, that if the atomic weight of 

 hydrogen was put as 1.00, the atomic 

 weights of the other elements became whole 

 numbers as follows : 



peout's atomic weights (1815 a.d.) (with the 



1915 atomic weights on hydrogen 



basis in parentheses) 



Hydrogen 1.0 (1.000) 



Carbon 6 (11.91) 



Nitrogen 14 (13.90) 



Phosphorus 14 (30.78) 



Oxygen 16 (15.88) 



Sulphur 16 (31.82) 



Calcium 20 (39.76) 



Sodium 24 (22.82) 



Iron 28 (55.41) 



Zinc 32 (64.86) 



Chlorine 36 (35.46) 



Potassium 40 (38.80) 



Barium 70 (136.31) 



Iodine 124 (125.94) 



If Prout 's atomic weights had proved ex- 

 actly correct, his claim that hydrogen is the 

 protyle {wpilirr) vXtj) or fundamental ele- 

 ment, might have seemed justified, but 

 when it was found that these weights were 

 very far from correct his hj^pothesis was 

 largely discarded. 



The prejudice which existed a few years 

 ago against Prout 's idea is well shown by 

 a quotation from von Meyer's "History of 

 Chemistry," printed in 1906. 



During the period in which Davy and Gay-Lus- 

 sac were carrying on their brilliant work, and be- 

 fore the star of Berzelius had attained to its full 

 luster, a literary chemical event occurred which 

 made a profound impression upon nearly all the 

 chemists of that day, viz., the advancement of 

 Front's hypothesis. This was one of the factors 

 which materially depreciated the atomic doctrine in 

 the eyes of many eminent investigators. On ae- 



