1S80.] and Refraction of light. 339 



It is perhaps worth notice that the result as to the change of 

 phase for the vibrations in the plane of incidence is independent 

 of the equation p — p ■ 



Since the above was written, I have found that Ketteler has 

 given in Wiedemann's Annalen, Vol. ill., Part 1, 1878, equations 

 from which the change of phase which accompanies total reflexion 

 may be deduced. 



Fehruary 23, 1880. 

 Professor Newton, President, in the chair. 



Lord Rayleigh, M.A., Professor of Experimental Physics, 

 William Burnside, M.A., Fellow of Pembroke College, John 

 Greaves, B.A., Fellow of Christ's College, and A. J. C. Allen, 

 B.A., Fellow of Peterhouse, were ballotted for and duly elected 

 Fellows of the Society. 



Professor Willie Kuhne, of Heidelberg, formerly of Amster- 

 dam, Adolf Erik Nordenskiold, Commander of the Swedish 

 Arctic expeditions of 1864, 1868, 1872—3, 1878—9, and William 

 Henry Flower, F.R.S., Hunterian Professor in the Royal College 

 of Surgeons of England, having been nominated by the Council, 

 were ballotted for and duly elected Honorary Members of the 

 Society. 



The following communications were made to the Society : — 



(1) Professor T. M'^K. Hughes, M.A., On the transport of 

 fine mud and vegetable matter bij conferva. 



It has, I dare say, been observed that often in warm summer 

 weather rivers, like the Cam above Cambridge for instance, or the 

 Lea near Hertford, run quite turbid, though generally bright and 

 clear. If we examine the bottom of such a stream we may notice 

 patches of velvety growth on the mud, and when the sun shines, 

 the oxygen given off by these plants is seen in sparkling bubbles 

 tangled in the fibres. If we watch, we see one mass after another 

 slowly disengage itself from the mud and rise to the surface of the 

 water, sometimes coming up edgewise when the little gas-floats are 

 more numerous on one side than another. Gas, probably car- 

 buretted hydrogen, sometimes appears to be let-out from the mud 

 below on the removal of the covering mat of conferva. The fine 

 mud lifted with the root end of the plant leaves it gradually as it 

 ascends, and when the process has been going on for some time, 

 the w^ater appears so muddy that it might be supposed that cattle 

 or ducks or men had been disturbing it higher up the stream. 



