1889.] On Selenic Acid and other Selenium Compounds* 13 



[On repeating the experiments after the Easter Vacation, an effect 

 was observed which may explain the difference between the value of 

 the wave-length along the wire found in the above experiments and 

 those of Hertz. It happened that the plates after the vacation were 

 placed further from the wall than they had been before, and it was 

 found that the wave-length was much less, being now between seven 

 and eight metres ; on moving the plates nearer the wall the wave- 

 length increased, the increase being evidently due to the increase 

 in the capacity of the plate produced by the proximity of the wall. 

 Thus if the distance of the plates from the walls was different in 

 the determination of the wave-length along the wire from what it 

 was in the determination of the wave-length through air, the wave- 

 lengths would not be equal even if the velocity of propagation were 

 the same. I endeavoured to determine the wave-length in air by 

 measuring the distance between the nodes after reflection from a 

 large metal screen, bat could not succeed in fixing the position of 

 the nodes with sufficient definiteness to determine the wave-length 

 with any accuracy. The fact, however, that I got a wave-length in 

 the wire the same as that obtained by Hertz through air, is sufficient 

 to show that it is not necessary to suppose that the velocities through 

 the wire and air are different, but that the difference in Hertz's results 

 may have been due to a change in the position of the vibrator rela- 

 tively to the walls of the room. — May 15.] 



II. "Researches in the Chemistry of Selenic Acid and other 

 Selenium Compounds " By Sir Charles A. Cameron, M.D., 

 F.R.C.S.I., Y.P.I.C., Professor of Chemistry and Hygiene, 

 R.C.S.L, and John Macallan, F.I.C., Demonstrator of 

 Chemistry, R.C.S.I. Communicated by Sir Henry ROSCOE, 

 F.R.S. Received April 6, 1889. 



Although selenic acid was prepared by Mitscherlich so far back as 

 the year 1827, few chemists appear to have studied its properties. 

 This want of interest in selenic acid is rather surprising, seeing that 

 it possesses so close a relationship to sulphuric acid, which is so 

 important a compound. Finding the chemistry of selenic acid so 

 meagre, we resolved to make an investigation of this body, with the 

 view of bringing, so far as we could, its chemistry abreast with that 

 of sulphuric acid, and also in the hope that its study would yield 

 results which might throw additional light on the relations of the 

 latter acid. The following pages contain the results at which we 

 have arrived. 



