118 
THE YOUNG SCIENTIST. 
bird doing something that you have pre- 
viously noted, don't omit it and say to 
yourself, " I've put that down," but make 
a note of it. This is the only way in 
which you can decide whether you have 
noted an oddity or not ; habits are sim- 
ply actions repeated. Among the aids to 
identification I will mention the "local 
list," and access to a good library. A 
local list " is a list of the birds that 
occur in a given locality, and is generally 
based on several years' observation in 
that locality : it helps by narrowing down 
your circle of search. In nearly every 
city or village is a public library, where 
you can find works on ornithology. 
The rising generation will furnish our 
future ornithologists ; but ]iiy greatest de- 
sire is to do what I can to make the study 
more universal, for none but good results 
can follow. 
Casting in Plaster of Paris —II. 
BY MAEK MALLETT. 
T will be w^ell to make some ar- 
rangement by which our cast 
can be hung up. We may bore 
two holes through the middle 
of the top rim of the mould, and put a 
loop of copper wire through them, bend- 
ing its ends so as to give them ii firm 
hold, and so arranging it that it will be 
well imbedded when the mould is filled 
with plaster. We use copi)er and not 
iron wire, because the latter would cer- 
tainly rust, and sooner or later cause the 
plaster to become discolored and split. 
The mould is now ready to be filled, that 
is, we may now proceed to make the ac- 
tual cast. Had our work been of a more 
particular nature we should now have 
used su]ierhne, but we have decided that 
fine plaster will serve our purpose. Still, 
whichever it may be, we must be partic- 
ular to mix it with the greatest care, by 
the rules already laid down. Clean water 
must be used. 'When ready the plaster 
must be poured into the mould, and the 
latter gently shaken and moved from 
side to side, so as to cause the fluid to run 
into every cranny, and to leave no air 
bubbles between mould and cast. The 
bellows may again be used to advantage 
to blow the plaster well into the under- 
cuttings. Lose no time till a covering 
has been given to the whole mould, for 
the liquid plaster will quickly thicken 
and begin to set, .and it will not then 
flow into corners and cuttings; go on till 
you have laid a, coating of fine plaster, a 
quarter of an inch or more in thickness, 
over every part of the mould, and then 
back up with coarse till your cast is thick 
enough. An unpracticed caster should 
not venture to leave his casts too thin ; it 
is false economy. They must be strong 
enough to resist the blow^ of the mallet 
used in chipping off the mould. The 
thickness must to a great extent be regu- 
lated by the size and nature of the model; 
for such a one as the present, three-quar- 
ters of an inch, in the weakest parts, will 
suffice. 
Almost directly after the mould is filled, 
i you can begin to smooth and trim off the 
back of the cast, for this you will do most 
easily whilst the plaster is still soft. By 
the time that this is done the cast will be 
hard enough for you to begin chipping 
away the mould. The cast should be 
laid on its back on a table or other suffi- 
cient support: if it can be placed in a 
sloping position it will be easier to work 
at, and the chips will fall away more 
readily. Your tools must be a mallet and 
a bluiit chisel. The edge of the latter 
should be ground off round. 
The outer mould and its irons will be 
easily and quickly removed. By a few 
bold strokes they can be fetched off in a 
few pieces, for the clay which has been 
daubed between them and the inner 
mould will cause the two to part readily. 
The outer mould being cleared away, we 
next have to remove the inner mould. 
We have now come to the most inter- 
esting i)art of the whole process. No' 
j small pleasure can be promised to the 
operator whilst with the removal of the 
inner mould he sees his model gradually 
reappear in a new, solid, and beautifully 
j white material. The inner mould must 
be chipped off in small pieces, and with 
I great care, lest injury be done to the cast 
[beneath. It is safer to keep the chisel, 
j whilst working, almost at a right angle to 
i the surface. And now the value of the 
j tinted mould will become apparent. The 
I difference of color will enable the oper- 
ator at once to distinguish between the 
mould and the surface of the cast, 
I when the latter is reached, and thus all 
I danger of cutting into the latter by mis- 
take will be avoided. If the directions 
' given are followed with care, the inner 
mould and cast will separate with suffi- 
cient ease, though not so freely as the 
outer and inner moulds had parted, 
A clean soft brush may be used to re- 
move chips from the surface, and the 
bellows will again be found useful to 
clear out hollows and under-cuttings. 
When the mould has been entirely re- 
moved, notwithstanding all our care, we 
can scarcely hope to find the cast wholly 
free from imperfections. Some project- 
ing part may have been chipped off, there 
may be holes caused by air bubbles, or 
others made by chance slips of the chisel. 
