The gases were passed through discs of paper, and the number of discs was increased so as to increase the obstruction, the pressure and quantity of gas remaining the same.
With one disc
of drawing-paper 6·5 cubical inches of hydrogen passed in 7′
6·5 „ „ of olefiant gas in 18′;
with two discs the hydrogen passed in 15′·4
„ „ olefiant gas „ 38′;
with three discs the hydrogen „ 22′·5
„ „ olefiant gas „ 57′·75.
Lastly, for the effect of obstruction, I used a tube filled with pounded glass. This was uncertain, because on moving the tube it was impossible, almost, not to move some of the particles within, and then, of course, circumstances were changed; but by sending the gases through one alter the other, results were obtained,
the mean of which gave for hydrogen 3′·4
„ „ for olefiant gas 4′·7.
It would seem from these experiments that mere obstruction is not the cause of the effect observed in tubes, for when the tubes are removed, and obstructions which retard much more placed for them, the effect is lost; and as the same aperture produces no difference of effect at high or low pressures, the variations between different apertures should probably be referred to some other cause.
I then endeavoured to ascertain some of the circumstances attending on tubes. Both glass and metal tubes produce the effect, and a metal tube, down which a wire had been thrust, did not seem to have this influence on the passage of gases through it altered. The effect is heightened as the gas is made to pass more slowly through the tube; and this, whether the increased time be caused by diminished pressure, increased length of tube, or diminished diameter. This may be well illustrated by putting several very fine tubes together, for the particular effect is thus increased whilst the time is shortened. Two brass planes were ground together, and a few scratches made down one of them so as to form very fine tubes; through these olefiant gas passed in 26′·2, and hydrogen in 32′·5.
Three glass tubes were taken of different diameter, and cut into such lengths that they passed nearly equal quantities of hydrogen gas in equal times hy the same pressure; their lengths were 42, 10·5, and 1·6 inches. The longer tube passed the
