21 
and water are regulated either by raising and lowering the 
bottles or by means of the cocks in the pipes. 
The tube is fixed in an ordinary retort-stand, so that the 
blast is vertical. If then a small splinter of wood is held 
downwards pointing into the spray, a lump of ice forms on 
the end of the splinter, and this lump has all the appearance 
of the hailstones. It is quite white and opaque, it is 
conical in form and has a rounded base and striated surface. 
In this way I have formed stones from half to three- 
quarters of an inch in diameter. When, however, the 
stones are growing large it is neccessary to move this 
splinter so as to expose in succession all parts of the face 
of the stone to the more direct action of the spray. 
When using this apparatus in a warm room I have found 
it best to fix a pad of blotting paper over the jet at a height 
of 10 or 12 inches. The surface of this pad is cooled by the 
spray and prevents radiation from the ceiling, which other- 
wise tends to melt the top of the stone. For a similar 
reason I have found it well to surround the blast with a 
wide clylinder or inverted cone of paper, which keeps ofi 
radiation without interfering with the action of the jet. 
By sticking several splinters of wood pointing downwards 
into the pad, a number of stones may be made at once. 
In the accompanying 
sketch a medium sized stone 
as well as one of the largest 
stones are shown attached 
to the splinters of wood. 
The surface of the cone, 
where continuous, is truly 
conical or rather pyramidal, 
but this surface is broken, 
as it were by steps, and a 
very marked fact is that all 
the continuous surfaces ha 
vertex, and hence the diffi 
