464 Scientific Intelligence. 



11. Change of Velocity of Cathode Rays in passing through 

 thin Metallic Layers. — H. Hertz first observed the passage of 

 these rays through thin metallic screens, and showed that the 

 rays were diffused in their passage. P. Lenard's paper on the 

 passage of cathode rays outside the exhausted vessel into air 

 and through various substances is well known. He found that 

 the rays apparently suffered no change in velocity. W. Seitz 

 came to the same conclusion. Lately E. Gehrcke showed that 

 under constant potential differences a homogeneous beam of 

 cathode rays after reflection from metallic surfaces showed itself 

 non -homogeneous and the beam was spread out into a spectrum. 

 G. E. Leithauser has extended this work to the study of the pos- 

 sible change of velocity which a homogeneous cathode beam 

 might suffer in passing through thin metallic membranes. He 

 points out that the failure of the earlier observers to notice a 

 change of velocity was perhaps due to their employment of Ruhm- 

 korf coils, and he has worked with a twenty-plate Holtz machine, 

 which gave a constant difference of potential. He thus obtains a 

 change in velocity and confirms Gehrcke's results. — -Ann. der 

 Physik., No. 12, 1904, pp. 283-306. J. t. 



12. Insulation in a Vacuum. — Lord Kelvin calls attention to 

 a confusion of ideas in regard to the conductivity of the ether. 

 He prefers to call the ether a very perfect non-resister of elec- 

 tricity passing through it, and, therefore, that the insulation of 

 electricity in a vacuum is to be explained not by any resistance 

 of vacant space or of ether but by a resistance of glass or metal 

 or other solid or liquid against the extraction of electrions from 

 it, or against the tearing away of electrified fragments of its own 

 substance. Lord Kelvin believes that it is quite true that the 

 extraction of an electrion from the atom is opposed by a definite 

 permanent force which must be overcome before the electrions 

 can be drawn out. He computes the order of such a force. 



Between electrodes -^ of a mm. apart raised to a difference of 

 potential of 200,000 volts the electrostatic force between them 

 will amount to 96,000,000 volts per cm. and would give a force 

 of 109*1 0~ 6 dynes or 16*6 tons per sq. cm. in the electrostatic 

 field ; four times the above electrostatic force, or 1,280,000 C. G. S. 

 units, would give a force of 66 -4 tons weight per cm. The break- 

 ing weight of the strongest steel wire scarcely amounts to 20 

 tons per sq. cm. Hence the metallic electrodes under considera- 

 tion would be broken into fragments. It would, however, bear 

 the 96,000,000 volts or 16*6 tons per sq. cm. 



Lord Kelvin believes it would be very desirable that careful 

 experiments should be made with steady current on the highest 

 obtainable vacuna. — Phil. Mag., Oct. 1904, pp. 534-538. j. t. 



13. Sloio Transformation Products of Radium. — Professor 

 Rutherford summarizes the successive changes of the various 

 emanations and constituents of radium and finds that certain sup- 

 posititious products of pitchblende which he calls radium D and E 

 should have very interesting rates of transformation. Radius D 



