TRANSACTIONS OF SECTION A. 489 



effective than dry sails (and particularly so in the case of old sails, and of sails of 

 thin and light material). 



An illustration was shown to the meeting by taking an Argand lamp-funnel, 

 with a piece of very fine closely-woven cotton cloth tied over one end of it. When 

 the cloth was dry, and the other end dipped under water, the water rose with 

 perfect freedom inside, showing exceedingly little resistance to the passage of air 

 through the dry cloth. When it was inverted, and the end guarded by the cloth 

 held under water, the water rose with very great freedom, sho-wdng exceed- 

 ingly little resistance to the permeation of water through the cloth. The cloth 

 being now wet, and the glass once more held with its other end under water, the 

 cloth now seemed perfectly air-tight, even when pressed with air-pressure corre- 

 sponding to nine inches of water, by forcing down the funnel, which was about 

 nine inches long, till the upper end was nearly submerged. When it was wholly 

 submerged, so that there was air on one side and water on the other the resistance 

 to permeation of air was as decided as it was when the cloth, very perfectly wet, 

 had air on each side of it. 



Once more, putting the cloth end imder water ; holding the tube nearly hori- 

 zontal, and blowing by the mouth applied to the other end : — the water which had 

 risen into the funnel before the mouth was applied, was expelled. After that no 

 air escaped until the air-pressure -wathin exceeded the water pressure on the outside 

 of the cloth by the equivalent of a little more than nine inches of water ; and when 

 blown with a pressure just a very little more than that which sufficed to produce a 

 bubble from* any part of the cloth, bubbles escaped in a copious torrent from the 

 whole area of the cloth. 



Water indicated by horizontal shading ; air by white paper. 



The accompanying sketch represents the application to the Navigational Depth- 

 gauge. The wider of the two communicating tubes, shown uppermost in the 

 sketch, has its open mouth guarded by very fine cotton cloth tied across it. The 

 tube shown lower in the diagram is closed for the time of use by a stopper at its 

 lower end. A certain quantity of water (which had been forced into it during the 

 descent of the gauge to the bottom of the sea) is retained in it while the gauge is 

 being towed up to the surface in some such oblique position as that shown in the 

 sketch. While this is being done the water in the wide tube is expelled by the 

 expanding air. The object of the cloth guard is to secure that this water is expelled 

 to the last drop before any air escapes ; and that afterwards, while the gauge is 

 being towed wildly along the surface from wave to wave by a steamer running at 

 fourteen or sixteen knots, not a drop of water shall re-enter the instrument. 



5. On the Effect of Oil in destroying Waves on the Siirface of Water. 

 By Professor Osboene Reynolds, M.A., F.B.S. 



This paper contauied a short accoimt of an investigation from -which it ap- 

 peared that the effect of oil on the surface of water to prevent wind-waves and 

 destroy waves alreadj' existing, was owing to the surface-tension of the water over 

 which the oil spread varying inversely as the thickness of the oil, thus introducing 



