THE YOUNG SCIENTIST. 
3 
that of a fowl occurred to Dr. Leidey. A 
man was found murdered by the roadside 
near Philadelphia, and a market-man 
was arrested on suspicion. His wagon 
ivas found stained with blood, which a 
microscopical examination proved to be 
human. His explanation of the blood- 
stains was that he had carried some 
grouse to market and their blood had 
soaked into the wagon-bed. The micro- 
scope showed positively and clearly that 
he lied upon this point, and the jury very 
properly convicted him of the murder. 
He afterwards confessed. ' 
In a future issue we will tell our readers 
Jiow to use their microscopes in the ex- 
iimination of blood, and will describe the 
best methods of showing that which is 
probably the most wonderful revelation 
in the whole field of science— the circula- 
tion of the blood in the veins of the living 
animal. 
Sharpening Wood-Working Tools. 
BY " OUR NED." 
DONT see how it is that I can't 
get my planes to work as nice! y 
as they used to do. They don't 
seem to be able to cut so sweet 
or make such silky shavings. I don't 
understand it. I sharpen and sharpen 
until I have nearly worn out my oil-stone, 
yet, although I make them sharp, I can 
not get good results." 
Such were the words of a young ama- 
teur friend of mine, who was the happy 
possessor of a good "kit" of amateur's 
tools, including a lathe, a good-sized 
scroll-saw, and a fine lot of carving tools. 
His complaint was made to me, with a 
request that I examine the tools and find 
out, if I could, where the trouble was, 
and to suggest such remedies as might, in 
my judgment, correct the evil. 
I examined the plane he particularly 
referred to, and found that the cutter iron 
was very dull and stubbed. This condi- 
tion of things was such that it was impos- 
sible to keep the cutter sharp, for the 
least wear on the cutting edge would be 
sufiicient to render the tool dull and inca- 
pable of doing good work, I show, in 
Pig. 1, the shape of the cutting iron as I 
found it. Now, by examining this figure, 
it will be seen that the cutting edge, a, 
when pushed forward, will work more 
like a scraper than a cutter, owing to its 
stubbedness, and that in fact the back of 
the basil, i e, the bevel of the iron 
at B, pressed against the wood at 
the back of the cutter, thus pre- 
venting it from performing its 
proper duties. To make this cut- 
ter right, and capable of doing 
its duty, I ground the tool until 
the basil assumed the shape as 
shown at Fig. 2. It will be seen 
that the cutting edge at a is more 
acute than at Fig. 1, and that the 
basil, B, in Fig. 2, is longer than 
at Fig. 1. It will also be noticed 
that on Fig. 2 there is a second 
Fig. 1. bevel, e. I explained the use of 
this second bevel to my friend as 
being quite necessary to insure good and 
effective work. I repeat the explanation 
here : If a cutter is ground down to its cut- 
ting edge, so that the line of the basil forms 
Fig. 2. 
an angle of 25° with the face of the tool, 
as shown at Fig. 3, then by examining the 
cutting edge, b, it will be seen that it pre- 
sents a very weak section, much too weak 
to be lasting or of much service. Indeed, 
Fig. 3. 
a plane-iron or chisel intended for general 
use, ground to this form, would be apt to 
crumble or "nip" out on the cutting 
edge, or if the temper is so fine that no 
crumbling takes place, the chances are 
that, in the case of a plane iron, it will 
"chatter" or spring and shake during 
