Intelligence and Miscellaneous Articles. 319 



the number 3265*8 nearly corresponded to the violet indium-line, the 

 number 3582 to the line H, and the number 3677 to the line H'. A 

 measurement of the positions of these lines on Pvutherfurd's photo- 

 graph of the solar spectrum gave nearly the same relative distances. 

 In addition to the lines above mentioned, several other lines were 

 visible in the indium spectrum ; but these belonged in part to the 

 gases of the atmosphere, and in part to the iron and zinc of which 

 the indium employed appears still to have contained traces, — a point 

 upon which light will be thrown by future experiments. 



Although the most recent determination of the equivalent of indium 

 by C. Winkler is probably tolerably near the truth, it did not seem 

 superfluous to ascertain its value by some other method. I selected 

 for this purpose the sulphide of indium, which 1 have found possesses 

 the very valuable property, for the object in view, of being com- 

 pletely converted by hydrochloric acid at the common temperature 

 into chloride of indium, with separation of sulphuretted hydrogen. 

 Chloride of indium, although extremely hygroscopic, can be accu- 

 rately weighed if certain precautions are observed ; and, in addition, 

 the proportion of sulphur can be accurately determined as a control 

 by leading the sulphuretted hydrogen that escapes into a solution of 

 a ferric salt, and determining volumetrically the quantity of ferrous 

 salt that is thereby produced. Contrary to what has been stated 

 hitherto, sulphide of indium is completely precipitated by sulphu- 

 retted hydrogen from any sufficiently dilute and not too acid solu- 

 tion. In colour, it cannot be distinguished from sulphide of cadmium ; 

 in fact indium in all respects exhibits the greatest similarity to cad- 

 mium, in relation to which its electrical behaviour requires it to be 

 classed as electro-negative. The results of the numerical determi- 

 nations have not yet assumed a final shape ; they will be contained 

 in the more detailed communication that is to follow. — Anzeiger d. 

 Kaiserl. Akad. d. Wissenschctft. in Wien, 1865, p. 139 (July 27). 



ON THE VISUAL SENSATIONS PRODUCED BY INTERMITTENT 

 EXCITATIONS OF THE RETINA. 



Professor E. Mach of Graz communicated to the Section of Natu- 

 ral Sciences of the Imperial Academy of Vienna, at its session on 

 July 20, a preliminary note on the effect upon the retina of the divi- 

 sion of the luminous stimulus with regard to time and with regard 

 to space. 



I. The luminous stimulus was examined when intermittent with 

 regard to time, and its useful effect for exciting sensation was mea- 

 sured. Both the intervals during which the light acted and during 

 which it was absent were varied in their absolute as well as relative 

 lengths ; and the results of the experiments permit of conclusions 

 being drawn as to the manner in which the vibrations of the retina 

 are excited and die out. 



II. If a rectangular strip of paper be painted with Indian ink so 



