GENERAL SUMMARY OF RESULTS. 89 



layer of the solution varying inversely as its concentral ion. The product of 

 the depth of layer times the concentration is a constant. If the solvent 

 plays no role in the absorption, then the transmission curves lor the different 

 concentrations of any given salts must fall directly over one another the 

 different curves would be the same curve. 



We found that, in general, the more concentrated the solution the less t be 

 transparency and the broader the absorption bands; this is exactly what we 

 obtained with the grating spectroscope and the photographic method. But 

 in the more dilute solution the intensity of the bands was greater. We 

 observed further, that with increase in dilution the middle of the band is dis- 

 placed towards the longer wave-lengths. 



The same general changes with dilution in the absorption spectra of solu- 

 tions of neodymium bromide were observed as with the chloride; the more 

 dilute the solution the narrower and more intense the bands. 



The bands of neodymium nitrate, in general, show the same changes with 

 dilution as those of the chloride and bromide. With increase in dilution the 

 intensities of the bands increase, and their centers are displaced somewhat 

 towards the longer wave-lengths. 



The three salts of neodymium, then, all show an increase in intensity with 

 dilution. A possible explanation of this phenomenon, based upon reson- 

 ance, has been offered. It is a well-known fact that a resonator, when excited 

 by vibrations from a single vibrating resonator having the same pitch, 

 vibrates more strongly than when set into vibration by a large number of 

 resonators, one of which has the same pitch as its own and the others slightly 

 different periods. In a word, if several vibrators are near together, every 

 one exerts a certain influence on the others. The result is that no one of 

 them has exactly the same period as the original resonator. Each resonator 

 damps the other and we have less perfect resonance. 



In a concentrated solution the resonators are relatively close together and 

 mutually affect one another. The result is imperfect resonance and the 

 absorption bands are less intense in the more concentrated solution. 



In the more dilute solution the vibrators are farther removed from ono 

 another and are surrounded by large amounts of water of hydration. The 

 damping effect would thus be diminished. In such cases we would have more 

 perfect resonance and the resulting absorption bands would be more intense. 



Subsequent work has, however, shown that a part of this effect can possibly 

 be explained as due to the fact that the slit-width used was not infinitesimal. 



It was found by the radiomicrometer, as with the grating spectroscope 

 and photographic plate, that for a given concentration the acetate absorbs 

 much more than any other salt of neodymium. 



One of the most interesting facts thus far established by means of the 

 radiomicrometer is the effect of the dissolved substance on the absorption 

 spectra of water. We noted that aqueous solutions of hydrated salts 

 were often more transparent than pure water. This is obviously a very 

 remarkable fact, and we at once took up its careful study. We compared 



