22 A STUDY OF THE ABSORPTION SPECTRA. 



lengths except the red, blue, and violet. When this was used no yellow 

 or green light fell upon the phosphorescing uranium salt, so that any light 

 in the yellow and green was necessarily due to phosphorescence and not to 

 reflection. A Fuess monochromatic illuminator was also used, sunlight 

 or arc-light being focused upon the slit of the illuminator. The salt was 

 placed in the beam of transmitted light. Usually the region of spectrum 

 used was 50 or 100 Angstrom units wide. The phosphorescent light was 

 viewed with the Hilger spectroscope. 



In the work on the Zeeman effect, the large electromagnet described 

 by Reese was used. This electromagnet has very large pole-pieces. A 

 cell to hold the solution was made of thin cover-glass plates about 1.2 by 

 1.2 by 0.3 cm. in size. The light from an arc or a Nernst glower was focused 

 upon the solution by means of lenses, and the emergent beam of light 

 focused upon the slit of the spectroscope. 



The concave grating described above was used for mapping the absorp- 

 tion spectra of solutions. A plane Rowland grating was also employed for 

 visual work in the second and third orders of the spectrum. For polar- 

 izing the incident light Nicol prisms were used. 



When anhydrous salts were employed they were dried in every case 

 by the best methods available. Thus, chlorides were dried in a current of 

 hydrochloric acid, bromides in a current of hydrobromic acid gas, and so on. 



The usual precautions were taken in working with nonaqueous solvents 

 to keep out all traces of moisture. Dehydrated salts were, of course, pro- 

 tected from contact with the air. 



An attempt was made to obtain the electrostatic Zeeman effect. For 

 solutions condensers made of ordinary cover-glass slides (used in mounting 

 sections for microscopic examination) were used. Aluminium foil was 

 placed between the glass slides in alternate layers. The solution (for 

 instance, neodymium chloride in glycerol) to be investigated was placed 

 between the slides between which there was no foil. For the production of 

 an electric field a Holtz machine was employed. This experiment was tried 

 for several solutions and for one gas, nitric oxide. In no case could any 

 difference be observed when the electric field was on and when it was off. 

 Further work is being done in this direction, especially on gases such as 

 iodine, bromine, nitric oxide, etc. In this way enormous electric fields 

 may be obtained, and it is not difficult to make the light pass either normal 

 or parallel to the electric field. 



In describing portions of the spectrum, red will be considered as extend- 

 ing from X 9000 to X 6500; orange from X 6500 to X 6000; yellow from X 6000 

 to X 5750; green from X 5750 to X 5000; blue from X 5000 to X 4500; indigo 

 from X 4500 to X 4250; violet from X 4250 to X 4000, and the ultra-violet from 

 X 4000 to X 1800. Rays of greater wave-length than X 9000 will be in the 

 infra-red. These rays include heat rays and " reststrahlen " and have been 

 extended to a wave-length of about 0.1 mm. Hertzian waves have been 

 explored from wave-lengths of many meters to that of about 6 mm., leaving 

 thus but a small gap between electromagnetic waves produced by ordinary 

 mechanical devices and waves produced apparently by molecular aggre- 

 gates. Waves of shorter wave-length than X 1800 will be designated as 

 Schumann waves. 



