Intelligence and Miscellaneous Articles. 383 



tiplying observations would be more fully experienced. Some 

 experiments for dividing up even the interval between two disks 

 have been begun, with promising results, but are not yet finished. 



It is well known that gazing steadily at a flickering surface is 

 trying to the eyes, but in the operations above described no incon- 

 venience whatever from this source was experienced, since if the 

 flicker was strong a glance revealed the fact and another disk was 

 substituted ; the faint flickering which demands more prolonged 

 attention seems to be no more trying to the eyes than ordinary 

 optical work. 



It may be a matter of some interest in physiological optics to 

 know that the sensation called " flickering " is independent of wave- 

 length and connected with change in luminosity. When two dif- 

 ferently-coloured surfaces of the same luminosity are successively 

 presented to the eye as above described, no shock is experienced, 

 and the colours are seen to mingle in a soft streaky way ; if obser- 

 vation is prolonged for some time, subjective effects begin to 

 manifest themselves, especially with quite low rates of rotation ; it 

 is of course best not to study these with undue curiosity. — American 

 Journal of Science, September 1893. 



EXPERIMENTAL INVESTIGATIONS ON DIELECTRICS. 

 BY DR. G. BENISCHKE. 



In the first part of the research the author determines the 

 dielectric constants of a few solid bodies by Gordon's method, as 

 modified by Lester, but in which, instead of the Ruhmkorff's coil, 

 the alternating current of the Innsbruck installation was used for 

 charging the condenser. This charges the condenser alternately 

 positively and negatively, so that the formation of residues of 

 either kind is thereby avoided. In order to attain greater sensi- 

 tiveness the alternating current was transformed into one of higher 

 tension by means of an induction-coil. In this way it was possible 

 to use various tensions. It was found that the dielectric constant 

 is independent of the strength of the electric field in the condenser ; 

 this also proves that there is no appreciable conductivity in the 

 dielectric, for if there had been its capacity must also have been 

 increased with increase of tension. The dielectric constant of 

 paraffin was found to be 1-89, ebonite 2*03, sulphur 2*42, ordinary 

 glass 4*17-4-52, plate glass 3*85. 



In the second part of the research the influence of the alternating 

 current on the dielectric constant was investigated, by exposing the 

 dielectric for various periods to tensions of 8 to 1600 volts, and 

 then investigating them. No such influence could be ascertained. 

 The capacity of the condenser was, it is true, 2 to 3 per cent, less, 

 but after a long time it reverted to the original amount. This 

 change may be ascribed to a transitory condition of strain, or to a 

 kind of hysteresis. — Wiener Berichte, April 13, 1893. 



