418 Scientific Proceecings, Royal Dublin Society. 
A spark about 5 mm. long, from a coil connected to Leyden 
jars, was passed in front of a tube open at both ends in which 
a light powder had been placed. The first spark caused the’ 
powder to arrange itself in little ridges, and at each succeeding 
spark the powder at these places was seen to jump up and settle 
down in the same places. When the tube was of small diameter 
the powder ascended quite to the top of the tube at each spark. 
The tube was thus effected throughout its entire length (about 
4 feet), and I could reflect into a second tube the air disturbance, 
causing a like effect in the other tube. The same effect could be 
produced in the open air, in which case the powder sprinkled on a 
card was observed to form rings round the place where the spark 
passed (rv.)." 
The same result was obtained by sharply tapping a mem- 
brane such as a piece of paper or indiarubber which had been 
tightly stretched over one end of a tube. In this case the heaps 
were separated by longer intervals (11.). 
In the above methods the shocks necessarily followed each 
other with comparative slowness, so that the effect was of short 
duration. By causing the air to vibrate by means of a reed-pipe 
a continuous effect was produced. In this case the far end of the 
tube had to be closed. With a small free reed-pipe, giving about 
1000 vibrations per second, beautiful laminee were produced. These 
were often seen to move en masse, just as the striee are often 
observed to do; this was owing to the fact that the intensity of 
the note was not quite constant, and also because the tube was not 
quite horizontal. On remedying these defects the lamine remained 
quite steady. Of course when the note ceased the powder fell 
down to the bottom of the tube. These lamine rose up a consi- 
derable height in the tube, and when its diameter was small they 
often reached quite to the top, so that when the sound was kept 
constant they appeared like so many little paper dises attached to 
the interior of the tube. The distance between the successive 
laminze was not quite constant, but was fairly so. It is evident 
that these laminze did not correspond to the nodes from the fact 
that the distance between them was nothing like what the formula 
(v = nl) would have demanded. Also the distance between them 
depended on the intensity of the note (r.). | 
These numbers refer to the figure on p. 417. 
