394 Scientific Intelligence. 



under electrical excitation of fluorescence continuous bands in the 

 green and also the red. Stokes' law apparently applies to the 

 fluorescence of metallic vapor, and the fluorescence ot the latter 

 aflords a means of explanation of various astrophysical phenomena. 

 — Ann. der Physik und Chemie, No. 3, pp. 447-453, 1896. j. t. 



7. Interference of Electric Waves. — Viktor von Lang 

 employs Quincke's well known double U-tube form of apparatus 

 for showing the interference of sound waves to exhibit also the 

 interference of electrical waves. Righi's apparatus is used to 

 generate short electric waves. These waves are sent into the 

 Quincke tube and by suitably changing the length of the arms of 

 the tube, interference is produced which is detected by a species of 

 coherer such as was used by Branly, and developed by Lodge. 

 One arm of the Quincke tube was also partially filled with certain 

 dielectrics and their index of refraction measured. The value ot 

 the latter for parafline was ja = 1 -701. Righi obtained \jl = 1*43. 

 For sulphur /u =. 2*333, while Righi obtained jjl = 1*87. — Ann. 

 der Physik und Chemie, No. 3, pp. 430-442, 1896. j. t. 



8. Pontgen^s Discovery. — Since the last issue of this journal 

 considerable progress has been made in the aft of cathode photog- 

 raphy. Greater detail has been obtained by what are called focus 

 tubes, which consist in the main of a modification of that form of 

 Crookes tube which was employed to show the convergence of 

 the cathode rays proceeding from a concave metallic mirror, upon 

 a thin sheet of platinum placed at its focus. When this sheet of 

 platinum is inclined at an angle of 45° to the line connecting the 

 cathode and the anode, it apparently serves as a center from which 

 sharp shadows are obtained. It seems probable also that the 

 anode reflects, the cathode rays in a similar manner. Tesla, 

 and O. N. Rood bring forward evidence to show that the 

 cathode rays can be reflected. Tesla early stated that it was 

 best to use one terminal of a high-frequency coil. I have found 

 this method of great advantage in diminishing the liability to 

 breakage of the tubes. A wire is led from one terminal of a Thom- 

 son or Tesla coil to one terminal of a Crookes tube, the other 

 terminal of which is connected to a large metallic plate. The 

 system should be brought into resonance. The method, however, 

 presents this difficulty. The high electromotive force and the 

 electrical oscillations drive out the occluded air and the tubes 

 require to be re-exhausted. It is desirable, therefore, to have the 

 tubes always connected with a mercury pump, or to exhaust the 

 tubes originally by the aid of a high-frequency coil. Tubes which 

 have been electrically excited by the ordinary Ruhmkorf coil 

 while being exhausted soon depreciate under the action of the 

 high-frequency coil. J. t. 



9. The Temperature of the Carbons of the Electric Arc. — 

 Wilson and Gray in a paper before the Royal Society give the 

 results of measurements of the temperature of the positive pole of 

 the electric arc. The temperature obtained was 



3600° abs. or 3300° C. 



