318 Intelligence and Miscellaneous Articles. 



of Professor Maxwell and Mr. Graham, that there is another effect 

 of air, namely, fluid friction, the coefficient for which they believe 

 to he independant of the tension ; and as far, therefore, as this effect 

 is concerned, little is gained by diminishing the amount of the 

 residual air. It would appear, however, that the fluid friction of 

 hydrogen is much less than that of atmospheric air ; so that, were 

 the heating effect due to fluid friction, it ought to be less in a 

 hydrogen vacuum. An experiment was made with this purpose ; 

 and, other circumstances being precisely similar, it was found that 

 in a hydrogen vacuum the heating effect due to rotation was 22'5, 

 while in an air vacuum it was 23*5. These numbers may probably 

 be considered as sensibly the same, and this experiment would 

 therefore appear to denote that the effect is not due to fluid friction. 

 15. The authors, in submitting these remarks to the Royal Society, 

 do not suppose that their experiments have yet conclusively decided 

 the origin of this heating effect, but they hope by this means to 

 elicit the opinions of those interested in the subject, which may 

 serve to direct their future research. 



XLII. Intelligence and Miscellaneous Articles. 



CONTRIBUTIONS TO THE KNOWLEDGE OF INDIUM. 

 BY PROFESSOR SCHROTTER. 



PURE metallic indium has the colour and lustre of cadmium ; it 

 is very soft, and marks paper easily, giving a bright streak with 

 only a slight shade of grey. 



The positions of the two characteristic lines of the indium spec- 

 trum were determined by direct comparison with the solar spectrum. 

 The spectrum of the metal was obtained in the usual manner by 

 means of a RuhmkorfF's induction-coil used in connexion with a 

 Leyden jar. The comparison showed that the magnificent blue in- 

 dium-line does not coincide with any of the dark lines of the solar 

 spectrum, and hence, according to Kirchhoff's acute deduction, that 

 no indium exists in the sun's atmosphere. This blue line corre- 

 sponds exactly with the number 2523 upon Kirchhoff's scale. The 

 second indium-line lies in the violet, between G and H, a part of the 

 spectrum which was only partially measured by Kirchhoff: it coin- 

 cides with a strong Fraunhofer's line, which is very sharply defined 

 on Rutherfurd's photograph of the solar spectrum. In order to de- 

 termine the position of this line with greater precision, the three 60° 

 prisms of the apparatus were first placed in the position of minimum 

 deviation for the line G (2854'8), and then the distances of the three 

 known lines, 2721, 2670, and 2574, were measured by means of 

 the micrometer- screw. In this w 7 ay the. value of a revolution of 

 the micrometer-screw was obtained in millimetres. On now mea- 

 suring in the same way the distances from G to the violet indium- 

 line, and to the lines H and H', keeping the prisms always in the 

 position of least deviation, it was found that upon Kirchhoff's scale 



