66 



NATURE 



[November 17, 1904 



1 



Thus, helium must be placed before lithium, and argon 

 before potassium, as is seen from the table, into which 

 radium has also been introduced. In this table there are, 

 in the group zero, two unknown elements, x and y, which 

 have been introduced for two reasons : first, because in the 

 corona of the sun, above the region of incandescent 

 hydrogen, there has been noticed an element which has an 

 independent spectrum, and therefore is named coronium ; 

 and although it is yet unknown (helium was also first 

 characterised by Crookes as an element, on account of the 

 independence of its spectrum), it must have a density, and 

 consequently an atomic weight, both smaller than those of 

 hydrogen (in the table, this element is marked as y) ; and 

 secondly, because there is no reason to believe that the 

 system of elements is limited in the direction of the lightest 

 ones by hydrogen. The presence of the elements x and y 

 in the group zero makes us think that the elements which 

 correspond to these positions in the system will be dis- 

 tinguished by the absence, in a high degree, of the capacity 

 of chemical combin- 

 ation — a property which 

 belongs also, as has 

 been already pointed 

 out, to helium, argon, 

 and their analogues. 



" The same property 

 must be attributed to 

 the substance of the 

 ether, which must 

 possess, moreover, an 

 e.xtremely low density, 

 and consequently a very 

 great rapidity of motion 

 of its molecules, in 

 order to have the possi- 

 bility of escaping from 

 the spheres of attrac- 

 tion, not only from the 

 atmosphere of the 

 earth, but also from 

 the atmospheres of our 

 sun and other suns the 

 masses of which are 

 greater than that of 

 ours. The researches 

 concerning the double 

 stars prove that the 

 masses of the stars 

 which we know do not 

 exceed the mass of our 

 sun more than thirty- 

 two times, while in 

 other cases they are 

 equal to it ; therefore, 

 if we attribute to the 

 ether the properties of 

 gases, we must admit, 

 on the basis of the 



kinetic theory of gases, that its specific gravity must be very 

 much smaller than the specific gravity of hydrogen. In 

 order that the ether may escape from the sphere of attrac- 

 tion of stars the mass of which is fifty times greater than j 

 the mass of the sun, it must, while it chemically resembles 

 argon and helium, have an atomic weight not more than 

 o 000 000 000 053 (and a density, in relation to hydrogen, 

 half as large, as I have proved in the above mentioned article 

 on ether). The very small value of this figure already 

 explains why there is little hope of isolating the substance 

 of the ether in the near future, as it also explains why it 

 penetrates all substances, and why it is condensed in a small 

 degree, or collects in a physicomechanical way, round ponder- 

 able substances — being mostly condensed round such 

 immense masses as that of the sun or of stars.' " 



In conclusion, Mendel^eff indicates that while the con- 



ception of the chemical elements is connected in the inost 

 intimate way with the generally received teachings of 

 Galileo and Newton about the mass and the ponderability 

 of matter, as also with the teaching of Lavoisier concern- 

 ing the indestructibility of matter, " the conception of the 

 ether originates exclusively from the study of phenomena 

 and the need of reducing them tu simpler conceptions. 

 Amongst such conceptions we held for a long time 

 the conception of imponderable substances (such as 

 phlogiston, luminous matter, the substance of the positive 

 and negative electricity, heat, &c.), but gradually this 

 has disappeared, and now we can say with certainty that 

 the luminiferous ether, if it be real, is ponderable, although 

 it cannot be weighed, just as air cannot be weighed in air, 

 or water in water. We cannot exclude the ether from 

 any space ; it is everywhere and penetrates everything, owing 

 to its extreme lightness and the rapidity of motion of its 

 molecules. Therefore such conceptions as that of the ether 

 remain abstract, or conceptions of the intellect, like the one 



71] 



which also leads us to the very teaching about a limited 

 number of chemical elements out of which all substances in 

 nature are composed." 



WELSH CONFERENCE ON THE TRAINING 

 OF TEACHERS. 

 'T'HE Welsh National Conference on the Training of 

 Teachers was held in Shrewsbury on November 10 

 and II, and although no special reference was made to 

 science teaching, still the subject of education is now in a 

 fair way to be considered a science, since it has been in- 

 cluded as a section of the British .Association. 



The conference was convened by the Central Welsh 

 Board and the University of Wales, and in addition to 

 these bodies, representatives attended from every county 

 education authority in Wales, from every type of educational 

 institution, from the National Executive of Welsh Councils 

 and from all the associations of masters and mistresses. 

 Upwards of 200 delegates attended in all, most of whom 

 remained throughout all four sessions. 



At the first session, which was devoted to " The Special 

 Aspect of the Problem of Training Presented in Wales," 



