TRANSACTIONS OF SECTION B. 601 



opposed to, nor did it invalidate, this evidence, because such an element as nitro- 

 gen not only emits two spark spectra, but the two spectra can be readily photo- 

 graphed simultaneously from the same spark discharge. 



It was proposed by M. de Gramont at the International Congress in Paris in 

 1900, and agreed, that no new substance should be described as an element until 

 its spark spectrum had been measured and shown to be difl'erent from that of 

 every other known form of matter. 



This appears to me to have been one of the most important transactions of 

 the Congress. The first application of this rule has resulted in the recognition 

 of radium as a new element : it is characterised by a special spark spectrum of 

 fifteen lines which have been fully studied and measured by Demarfay. It shows 

 no lines of any other element. 



Another application of this rule has recently been made by Exner and 

 Haschek with preparations of the oxide of an element obtained by Demar^ay, and 

 named europium. It exhibits 1193 spark lines and 257 arc lines. 



I have already mentioned that one feature strikingly shown in the spectra of 

 chemically related elements was the wider separation of the lines in pairs, triplets, 

 or other groups ; and that this was in some way related to the atomic mass, since 

 the separation Was greater in those elements whose atomic weights were greater. 

 Kayser and Runge, and also Rydberg, have shown that in the series of alkali metals 

 the atomic weights are very nearly proportional to the squares of the differences 

 between the oscillation frequencies of the lines, that is to say, the squares of 

 the intervals between the lines. Runge and Precht have recently shown that 

 in every group of elements that are chemically related the atomic weight is 

 proportional to some power of the distance separating the two lines of the pairs 

 of which the spectrum is constituted. In other words, if the logarithms of the 

 atomic weight and distance between the lines be taken as coordinates the corre- 

 sponding points of a group of elements which are chemically related will lie on a 

 straight line. Applying this law to the determination of the atomic weight of 

 radium they find that the strongest lines of the new element are exactly analogous 

 to the strongest barium lines, and to those of the closely related elements mag- 

 nesium, calcium, and strontium. The intervals between the two lines of each pair 

 in the principal series, and in the first and second subordinate series, if measured 

 on the scale of oscillation frequencies, are equal for each element, and the same 

 law holds good for the spectrum of radium. From this the value 257-8 was found 

 for the atomic mass of the element. This does not quite accord with the number 

 obtained by Madame Curie, who found it to be 225. It will be interesting to see 

 which number will eventually be proved to he the more correct. 



It isnow many years since I first pointed out that the absolute wave-lengths 

 of the lines of emission spectra of the elements are physical constants of quite as 

 great importance in theoretical chemistry as the atomic weights ; in the light of 

 recent discoveries this statement may be said to be now fully justified. 



Radio-active Elements. 



From the study of rays of measurable wave-lengths we have lately sailed 

 under the guidance of M. Henri Becquerel into another region where it is doubtful 

 whether the rays conform to the undulatory theory. In fact the rays are believed 

 to be charged particles of matter, charged, that is to say, with electricity. Beyond 

 doubt they are possessed of very extraordinary properties, inasmuch as they are 

 able to penetrate the clothing, celluloid, gutta percha, glass, and various metals. 

 They are, moreover, endowed with a no less remarkable physiological action, pro- 

 ducing blisters and ulcerations in the flesh which are difficult to heal. It is an 

 established fact that such efiects have been caused by only a few centigrams of 

 a radium compound contained in a glass tube enclosed in a thin metallic box 

 carried in the pocket. 



From this we can quite understand that there is no exaggeration in the 

 statement attributed to the discoverer. Professor Curie, by Mr. W. J. Hanmer, of 

 the American Institute of Electrical Engineers, that he would not care to trust 



