464 



Mr. W. H. Preece. On the 



[Apr. 3, 



to outbalance all the weighty chemical and physical differences 

 between them." 



The nature of the evidence derived from the spectroscope is here 

 quite misrepresented ; probably it was not well understood because of 

 its novelty. 



I have found that the spectra of magnesium, zinc, and cadmium are 

 the result of three series of harmonic vibrations with similar intervals, 

 the fundamental vibrations of which differ only in pitch. I have made 

 some similar observations with regard to copper, silver, and mercury, 

 aluminium, indium, and thallium, calcium, strontium, and barium, 

 though maps of some of these spectra have not yet been published. I 

 believe that in series of elements such as these, which exhibit grada- 

 tional differences in properties and in the properties of their compounds, 

 and approximately equal numerical differences in their atomic weights, 

 we are dealing with the same kind of matter in different states of 

 condensation, or in other words, with matter having similarly con- 

 stituted molecules, the vibrations of which are in the same direction 

 and at similar intervals but with different velocities. 



If we attempt to classify beryllium in accordance with the views of 

 Kilson and Pettersson, the elements scandium and yttrium, with 

 atomic weights 44 and 89 respectively, must yield spectra charac- 

 teristic of the series of which aluminium is the fh*st member, but it is 

 not possible to find a place for beryllium in this group, nor in those 

 to which cerium, lanthanum, and didymium belong ; it is, in fact, by 

 a process of exclusion first and selection afterwards that the element 

 falls into the dyad series. 



In the position which I assign to beryllium, we can account for it 

 being related, through the properties of its compounds, to magnesium 

 and zinc on the one hand, and to aluminium on the other. 



If there is one consideration of greater importance than another 

 which should lead to the determination of the position of an element 

 in a series, it is the mode of vibration of the molecule, and of that we 

 have evidence in the spectrum. When the element is one with a low 

 atomic weight there is no difficulty in interpreting such evidence. 



II. "On the Heating Effects of Electric Currents." By 

 William Henry Preece, F.R.S. Keceived March 19, 1884. 



The production of heat in electrical conductors due to the trans- 

 ference of electricity through them has become a matter of very great 

 practical importance. A knowledge of the variation of the law, due 

 to the dimensions and character of the conductor, is essential for 

 lightning protectors and for the leads of electric lights. 



