41 
arms extended, was to allow them to spread out in water on a glass slip, 
and then to drop some gum upon them, which killed the polypes instan- 
taneously, without allowing them to retract their tentacles. The gum 
could be subsequently dissolved off, and the specimens mounted in the 
usual way in any preservative fluid. 
Mr. Wm. Lant Carpenter, B.A., B. Sc., read the following note 
(illustrated by a diagram) on the Formation of Air-bubbles in Ice : — 
Having frequently occasion to obtain a temperature below 32° Fah., I am in 
the habit of employing as an easily made and cheap freezing-mixture, a mixture 
of crystallised sulphate of soda and hydrochloric acid. During the late severe 
weather, however, I made a mixture of snow and salt, which produced a tempera- 
ture slightly below 0° Fah. Wishing to test its efficacy, I immersed in it a small 
cylindrical vessel of pure water, and was surprised to notice the form taken by the 
lump of ice, which is illustrated by the diagram. It will be observed that the ice 
has, as it were, piled itself up into a small pyramid or cone on the centre of the 
top of the cylinder, the expansion which, you will remember, always occurs on 
freezing, having taken this form, probably because the cold was so intense that a 
portion of the water froze to the side of the vessel before there was time for the 
whole mass of tbe water to cool down to 39° and then to begin to expand 
regularly. 
The most curious point, however, in this experiment, was the way in which the 
air- bubbles arranged themselves in the congealed mass. Accidentally, the whole 
apparatus was placed in a room, the floor and walls of which were in a constant 
state of vibration from some machinery in motion ; consequently the particles of 
the water were very far from being at rest, and their line of motion seems to have 
been very plainly marked out by the air-bubbles. You will observe that these 
are arranged radially (like the spokes of a wheel), a small space in the centre only 
being at all irregular and confused, — and not only are the bubbles radial in their 
grouping, but to a large extent also in their shape ; for, instead of being spherical 
or only slightly ovate, they are in most cases lengthened out until they have 
become as much as 15 times as long as they are wide and thick, and the direction 
of this greatest length is always between the centre and the circumference of the 
cylindrical block. To assure myself that this arrangement obtained through the 
whole block, 1 spilt it longitudinally and transversely, and was greatly surprised 
at the extreme regularity of the radial lines of air-bubbles, only about roth of 
the cylinder, and that in the centre, being at all irregular in structure. I was un- 
able to satisfy myself whether the air-bubbles were very elongated ellipsoids, or 
parallelopipeds with curved surfaces at the two ends. 
One other small point deserves notice. In watching the block of ice, as it 
stood in a warm room, the air of which was about 52° Fah., and which, without 
being very damp, yet contained a considerable percentage of watery vapour, I 
noticed that the air within 0*5 inch of the ice was so saturated with moisture as 
to resemble vapour or fog, and the currents of air thus rendered visible by the 
vesicles of water, appeared to be moving downwards, parallel to the sides of the 
cylindrical block. Whether this was caused by vapour rising from the ice, or 
