Chemistry and Physics. 159 



pulses. He makes such a coherer out of comparatively fine carbon 

 powder. By means of such a coherer he obtained evidences 

 of interference phenomena. With a sensitive coherer filled with 

 nickel filings he measured the dimension of electric waves 

 produced by interference in passing through a metallic grating. 

 — Wied. Ann., No. 13, 1898, pp. 1024-1029. j. t. 



11. Color Blindness and the Rontgen Mays. — E. Dorn has in- 

 vestigated the sensitiveness of the eyes of a totally color-blind 

 person to the Rontgen rays. He believes that the light seen by 

 the color-blind person when the eye is exposed to the rays is not 

 due to a fluorescence excited in the retina by these rays, but is due 

 to a peculiar aptitude of the eyes to perceive these rays. The 

 light excited by the rays is greatest at the periphery of the eye; 

 this indicates that the rods of the eye are sensitive to the Ront- 

 gen rays. The author then sought to answer the question 

 whether the cones are also sensitive. He discovered that these 

 are also sensitive and no central blind spot insensitive to these 

 rays could be found in the totally color-blind eye. His experi- 

 ments he believes can be used to disprove the hypothesis that 

 total color-blindness can be ascribed either to failure or the apti- 

 tude of the cones of the eye. — Wied. Ann., No. 13, 1898, pp. 1170- 

 1176. j. t. 



12. Regenerating Vacuum Tubes; by W. Rollins. (Com- 

 municated.) — In an interesting article in the January number of 

 this Journal on absorption of gases in a high vacuum, Prof. C. C. 

 Hutchins states that after a short period of work the vacuum in 

 a Rontgen tube becomes too high. He then considers the causes 

 of the rise and discusses the various methods for increasing the 

 pressure, recommending oxygen as the most suitable gas because 

 its absorption is slow. The use of oxygen is not new ; tubes with 

 adjustable oxygen vacuums were made soon after Rontgen's 

 discovery was announced and were described in a series of notes 

 on Rontgen light in the Electrical Review in 1897-8, and are illus- 

 trated in Kirmayer and Oelling's catalogue. In this connection it 

 may be well to state that regenerative tubes with hydrogen vacuums 

 have been recently recommended by Villard, who attaches a closed 

 platinum tube which is heated in a Bunsen flame when it is de- 

 sired to increase the pressure in the Rontgen tube. A regener- 

 ating tube of this kind was described in 1897'in the above-men- 

 tioned notes, which was superior to the more recent form, because 

 the hollow platinum tube was used as a target for the impact of 

 the cathode discharge. As this hollow target could be cooled, a 

 large amperage could be used. To increase the pressure it is 

 only necessary to put a drop of liquid hydrocarbon into the hol- 

 low target and heat it with the cathode discharge, or illuminating 

 gas can be used, retaining it temporarily in place with a bit of 

 cork. 



In some of my experiments I tried a plan used by Professor 

 Trowbridge soon after Rontgen's discovery was announced, but 

 now lost sight of, which consisted in cooling the discharge tube 



