268 
THE YOUNG SCIENTIST. 
one for setting the jaws to the thickness 
of the teeth, which is effected by a stop 
held by the thumb-screw/; and the other 
for determining the angle to which the 
teeth shall be bent, which is regulated by 
the thumb-screw g. 
Fig. 3 is so constructed that it may be 
stuck in a hole in 
the work-bench. 
The punch C is 
p i V o t e d t o the 
stock, and is 
struck by a ham- 
mer. The gauge 
D, against which 
the points of the 
teeth rest, gradu- 
ates the position 
of the saw in ac- 
cordance with the 
length of the teeth and in relation to the 
hammer. The blade rests on H, whose 
vertical adjustment determines the de- 
gree or set. 
Fig. 4 is another form of bench imple- 
ment, in which the punch is placed in a 
socket of the adjustable spring. The saw- 
rest has an inclined lower side, and the 
Fig. 3. 
Fig. 4. 
brackets vary in elevation to suit, so that 
the rest can be moved endways to alter 
its elevation and the set of the saw, such 
movement not destroying the horizon- 
tality of the upper edge of the rest. 
Fig. 5 shows another set suitable for 
putting in a bench. It is on the hammer 
principle, and can easily be adjusted to 
give the requisite set by raising or lower- 
ing the two set-screws. 
Hand-saws may be set very well with a 
small punch or nail-set. Place the blade 
of the saw on a piece of hard wood ; then 
take a small punch, i^utting the flat end 
of it on the tooth to be set ; strike the top 
of the punch a short, sharp blow. Ex-^ 
amine the tooth ; if all right, go over th& 
Fig. 5. 
other teeth in a like manner, giving each 
tooth the same sharp blow. If the set is 
too much, strike lighter; if too little, 
strike heavier. Go over every other tooth 
first ; then turn the blade over and repeat 
the process. 
Sufficient has now been said on the sub- 
ject of saws, in this journal, to enable the 
amateur to file his own saws tolerably 
well; but should he need further infor- 
mation he may obtain it from a work re- 
cently published by the proprietors of 
this journal, entitled Hand-Saws, their 
Use and Abuse ; How to Select and How 
to File." Price $1.00. I have drawn 
freely from the work in the foregoing 
papers. 
»-^_a 
Breguet. 
N days gone by, the clepsydra, 
the sun-dial and the hour-glass 
were used to record the flight 
of time. The clepsydra was a 
transparent case filled with liquid which 
slowly trickled through an aperture in 
the bottom, the receding waters marking 
the passage of the hours, which were in- 
dicated by characters traced upon the 
glass. This was the oldest and simplest 
form of the clepsydra ; and the hour-glass 
was but a modification of the same princi- 
ple, sand being substituted for water. 
The advantages of the hour-glass over 
