102 
THE YOUNG SCIENTIST. 
be made. 1. The egg may contain an 
embryo. 2. Suppose the egg may get 
cracked or broken during tlie operation of 
blowing it. 
If the former is the case, you must re- 
move the embryo, if possible. There are 
several ways of doing so, the usual one 
being to obtain a small pair of scissors 
with long thin blades, and, inserting 
them through the hole, cut the embryo to 
pieces, and hook it out with a crooked pin 
or some such instrument. There is also 
another way of which I have read, but I 
would not advise any collector to attempt 
it, especially with a rare egg. This is to 
paste a piece of paper over the hole in the 
egg, first making a corresponding hole in 
the paper to fit the one in the egg ; then 
lay the egg on an ant hill and the ants 
will do the rest — i.e., eat the embryo and 
leave the shell ; but you must be sure and 
paste the paper on as above described, or 
the ants will be likely to eat the shell 
around the hole, and so spoil it for a good 
collection. If the egg should be cracked, 
you had better mend it as soon as possi- 
ble, or you will run the danger of crack- 
ing it more. There is a certain cement 
used for this purpose, but I have never 
tried it, as I have always mended my 
cracked or broken eggs in this simple 
way : Put a thin strip of tissue paper or 
court plaster (white would be best) and 
paste it over the whole length of the 
crack, or enough to prevent it from crack- 
ing more. 
Filing Saw Teeth. 
Most amateurs find great difficulty in keeping 
their saws in good order. Tlie following direc- 
tions will be found valuable, although some of 
them apply only to larger saws than are likely 
to be used by amateurs. They have been pre- 
pared by Mr. J. E. Emerson, member of a well- 
known firm of saw manufacturers : | 
The greatest wear of a saw is on the under 
sides of the teeth. File nearly to an edge (but 
not quite), leaving a short bevel of say 1-32 of 
an inch wide on the under side of the point. 
But in no instance file to a fine point and thin 
wire edge. 
1st. Be sure that the saw hangs properly on 
the mandrel. 
2d. The saw must be in proper line with the 
carriage, and the carriage run true. i 
3d. The mandrel must be level and run tight 
in the boxes. 
4th. Round off the saw so that all teeth will 
cut the same amount, and be sure that the very 
points of the teeth are widest. 
5th. Do nearly all the filing on the upper sides 
of the teeth, and see that they are well spread 
at the points ; file square, and have them pro- 
ject alike on botli sides of the saw. 
6th. If tlie saw heats in the centre when the 
mandrel runs cool in the boxes, cool it off and 
line it into the log a little. 
7th. If the saw heats on the rim and not in the 
centre, cool it off and line it out of the log a 
little. 
8th. Do not try the experiment of bending 
each alternate tooth for the set, when using in- 
serted toothed saws. 
9tli. File the teeth hooking, so that the swage 
will spread them at the points. 
10th. Use a light hammer in sw^aging, say 
three-quarters to one pound weight. 
In filing solid toothed circular saws, keep the 
throats or roots of the teeth round, or as the 
saws are when new. Angles, or square corners, 
filed at the roots of the teetli, will almost in- 
variably cause a saw to crack ; the filing of such 
angles or square corners will cancel the warrant 
on any saw. The back or top of the tooth leads 
or guides the saw, and should be filed square 
across. These directions, if carefully followed, 
will put the saw in excellent condition for cut- 
ting, and serve to keep it true in circumference, 
and even in balance. 
Luminous Paint. 
The London Building News says : " The com- 
paratively recent discovery that luminous paint 
can be applied as ordinary whitewash, con- 
siderably expands the field of its usefulness. 
Sheets of glass coated with the paint form Alad- 
din's lamps, which are in use in some of the 
vessels of the navy, at the Waltham Powder 
Factory, at Youngs Paraffin Works, and in the 
spirit vaults of several docks ; but now that, by 
increased production and the use of water as the 
medium, the cost is reduced by one-half, it will 
probably be extensively used for painting walls 
I and ceilings. The ordinary form of oil paint 
has already been applied in many ways to 
clock-faces, to name-plates and numbers on 
house-doors, and to notice boards, such as 
'mind the step,' 'to let,' etc. The paint emits 
light without combustion, and therefore does 
not vitiate the atmosphere. Several experi- 
mental carriages are now running on different 
railways, the paint being used instead of lamps 
AA'hich are necessarj' all day on account of the 
i line passing through occasional tunnels. It is 
