838 



SCIENCE 



[N. S. Vol. XXXVI. No. 937 



Crookes dark space, and finally the formation 

 of cathode and X-rays. The phosphorescence 

 due to the latter is strikingly shown by intro- 

 ducing into the bulb a few cubic centimeters 

 of willemite flour (W in the figure). This 

 should be well dusted over the inner surface 

 of the bulb before sealing the apparatus to 

 the pump. A particularly beautiful effect, 

 at the cathode-ray stage, is to disconnect the 

 pump and then shake the bulb vigorously so 

 as to throw the flour through space while the 

 discharge is passing. 



It may be of interest to add that the tube 

 works well on direct current of fairly low 

 voltage. For that purpose ordinary high 

 potential storage cells (of capacity one tenth 

 ampere normal discharge rate) may be em- 

 ployed. To guard against too great a current 

 flowing through the discharge tube an adjust- 

 able water resistance should be included in 

 the storage-battery discharge circuit. The 

 effect upon the ease with which the storage 

 battery discharge passes through the tube may 

 be nicely shown by first ionizing the remain- 

 ing gases in the tube by means of the high 

 potential induction coil discharge, and then 

 switching instantly to the storage cells. The 



minimum direct-current voltage that will, for 

 a given pressure, produce a discharge may 

 thus be obtained. This minimum voltage 

 together with other data and remarks are 

 given in the accompanying table. 



Chas. T. Knipp 

 Laboratory of Physics, 

 University of Illinois 



THE CONVOCATION WEEK MEETINGS OF 

 SCIENTIFIC SOCIETIES 



The American Association for the Advance- 

 ment of Science and the national scientific 

 societies named below will meet at Cleveland, 

 Ohio, during convocation week, beginning on 

 December 30, 1912. 



American Association for the Advancement of 

 Science. — President, Professor Edward C. Picker- 

 ing, Harvard College Observatory; retiring presi- 

 dent, Professor Charles E. Bessey, University of 

 Nebraska; permanent secretary, Dr. L. O. Howard, 

 Smithsonian Institution, Washington, D. C. ; gen- 

 eral secretary, Professor H. E. Summers, State 

 College, Ames, la. ; secretary of the council. Pro- 

 fessor H. W. Springsteen, Western Eeserve Uni- 

 versity, Cleveland, Ohio. 



Section A — Mathematics and Astronomy. — Vice- 

 president, Professor E. B. Van Vleck, University 

 of Wisconsin; secretary. Professor George A. 

 Miller, University of Illinois, Urbana, 111. 



Section B — Physics. — Vice-president, Professor 

 Arthur Gordon Webster, Clark University; secre- 

 tary. Dr. W. J. Humphreys, Mount Weather, Va. 



Section C — Chemistry. — Vice-president, Pro- 

 fessor W. Lash Miller, University of Toronto; 

 secretary. Professor C. H. Herty, University of 

 North Carolhia, Chapel Hill, N. C. 



Section D — Mechanical Science and Engineering. 

 — Vice-president, Dr. J. A. Holmes, U. S. Recla- 

 mation Service; secretary, G. W. BisseU, Michigan 

 Agricultural College, East Lansing, Mich. 



Section E — Geology and Geography. — Vice-presi- 

 dent, Professor James E. Todd, University of 

 Kansas; secretary, Professor G«orge P. Kay, Uni- 

 versity of Iowa. 



Section F — Zoology. — Vice-president, Professor 

 William A. Locy, Northwestern University; secre- 

 tary. Professor Maurice A. Bigelow, Teachers Col- 

 lege, Columbia University, New York City. 



Section G — Botany.- — Vice-president, Professor 

 D. S. Johnson, The Johns Hopkins University; 



