PHYSICS — WOOD, ZAHM. 257 



The bright-line rotation spectrum of absorbing vapors. — With the 

 apparatus described in the previous section a very remarkable phe- 

 nomenon appears when the vapor has considerable density. Light 

 from the arc is passed through a nicol prism, the steel tube containing 

 the sodium (which traverses the magnet), and a second nicol set for 

 extinction. On exciting the magnet the system transmits light 

 which the spectroscope shows to be made up of a multitude of fine 

 lines in the red and blue- green region. Over a hundred lines can be 

 counted in the red region of the spectrum formed and about the 

 same number in the blue-green region. These lines have been 

 photographed with a 14-foot concave grating and found to coincide 

 with absorption lines, the significant fact being, however, that com- 

 paratively few of the absorption lines are represented in the rotation 

 spectrum. Just why this is so is not apparent. The rotatory power 

 of an electron is probably inversely proportional to its mass. The 

 lighter the electron in proportion to its charge, the greater will be the 

 perturbations in its orbit produced by the magnetic field. Possibly 

 the absorption lines which exercise rotatory power result from the 

 negative electrons of small mass, while the other absorption lines 

 are due to heavier corpuscles, perhaps carrying positive charges. 



The fact that the bright lines of the fluorescence spectrum appear 

 to coincide with those of the magnetic rotation spectrum favors this 

 hypothesis ; for we should expect the lighter electrons to be set in 

 more violent vibration by the light waves than the heavier ones. A 

 further study of the phenomenon will doubtless throw more light on 

 the subject. Iodine vapor also gives a very beautiful bright line 

 spectrum. 



Zahm, Albert F., Catholic University of America, Washington, Dis- 

 trict of Columbia. Grant No. 272. Determination of resistance 

 of air to moving bodies. $1,000. 



Abstract of Report. — Prof. Zahm reports that he has perfected a 

 delicate balance for suspending bodies in the wind-tunnel, has meas- 

 ured the atmospheric resistance of a variety of spindle and hull shapes, 

 particularly those of fair outlines, and has also measured the resist- 

 ance of posts, rods, and wires, such as may be used for the bracing 

 of structures and are to be exposed to the impact of the wind. He 

 hopes to publish the results during the coming year. 



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