524 REPORT-^ 1881. 



6. On some applications of Electric Energy to Horticultural and AgricultufaX 

 purposes. By Dr. C. Wm. Siemens, F.B.S. See Reports, p. 474. 



7. On Hydrocarbons in the Solar Atmosphere. By Captain Abney, B.E.^ 



F.B.8. 



The existence of hydrocarbons in the solar atmosphere depends upon the evi- 

 dence of the absorption-spectra in the iiifra-red I'egion of certain hydrocarbons,, 

 which ha-\'e been photographed lately by the author, in conjunction with Colonel 

 Pasting, R.E. In these spectra certain lines were mapped, which, when a large 

 dispersive power was used, coincided with Fravmhofer's lines in the solar spectrum, 

 agreeing with them, not only in position, but also in relative intensities. That the 

 hydrocarbons are not due to our own atmosphere was shown by the fact that the 

 relative intensities did not vary with a high as compared with a low sun. The ' a ' 

 group of lines in the solar spectrum was also pointed out as containing lines due to 

 the hydrocarbons; but that, as- they were faint lines, they would not materially 

 affect the validity of any argument which might be brought against the theory 

 should it be shown that this region altered in intensity with a high and low sun. At 

 the same time this group shoidd be carefully examined to see if the lines varied in in- 

 tensity whilst others remained constant. The similarity of the fundamental band of 

 the benzene series to the A and B lines was also noticed. The A. line was doubtless 

 solar, whilst the B line was, according to observation by careful spectroscopists, of 

 telluric origin. Should it eventually prove that the A and B lines were due to 

 hydrocarbons, one would be present in the sun and the other in our own atmo- 

 sphere. To carbonic acid the latter could not be referred, since the absorption due 

 to that gas in a length equivalent to more than that found in the atmosphere had 

 been taken and gave absolutely no lines. If future observations showed the existence 

 of hydrocarbon vapour in the solar regions, a very interesting problem in solar 

 physics was opened out, to which attention would be given by the author and, he 

 hoped, other observers, in the immediate future. 



FRIDAY, SEPTEMBER 2. 

 The Section subdivided and the following Papers and Report were read : — 



PHYSICAL DEPARTMENT. 



1. On Surface-tension and Capillary Action. By Professor^OsBOKNE 



Reynolds, F.E.S. ^'-^r^ 



In the first place it was pointed out that, although surface-tension has hitherto 

 been considered as a statical or hydrostatical force only, such actions as the spread- 

 ing of oil upon water exhibit phenomena, and those of a very marked kind, which 

 depend, not on a statical force, but on the maintenance of this force while the sur- 

 face is contracting at a very high velocity. And, in the second place, it was pointed 

 out that the assumptions on which Laplace's theory of surface-tension is founded 

 are insufficient to explain these phenomena, which suggest certain relations between 

 the range of the inter-molecular attractive forces and the dimensions of these 

 molecules. 



It was shown that if the surface of pure water be touched at some point with a 

 slightly oiled needle, the oil spreads out quickly in a circular patch, which patch at 

 first extends with great rapidity. But it was not the rapidity of extension that was 

 so much the point of remark, as the motion of the surface of the pure water before 

 the advancing oil. In the iisual way this motion is shown by a rib or slight eleva- 

 tion of the water immediately at the edge of the oil. When the initial surface is 

 very clean the rib is always formed, but it only becomes apparent under peculiar 

 circumstances. It is often apparent on the surface of a deep pool formed at a 



