20 
THE YOUNG SCIENTIST. 
" Well, Pa, I will be satisfied with the 
number of rooms you say, but you will 
make the rooms large, won't you ?" 
" Yes," said her father, " we will make 
them a good si^e. We will have the 
parlor 18 inches long by 14 inches wide, 
and the dining room 12 inches by 18 
inches, and two bed rooms in the second 
story the same size as the rooms down 
stairs. We will make the lower hall ten 
inches wide, and the upper hall the same 
width. The length of both halls will be 
the same as the length of rooms, eighteen 
inches. Now, if we imagine these lengths 
and widths to be in feet instead of inches, 
it would make the house appear to us to 
be a pretty large one. In fact, I intended 
that the house shall be built on the scale 
of one inch to the foot, or in other Words, 
each inch on the play house, in any direc- 
tion, will represent one foot of a real 
house — thus : the 18 inches which show 
the length of the parlor will represent 
18 feet, thus showing the room to be 14 
by 18 feet. We may consider the house 
we are about to erect as one-tw^elfth 
the actual size of a house whose di- 
mensions are on the ground plan, 
eighteen feet by thirty-six feet. If you 
study this matter a little, you will under- 
stand why it is that architects and 
engineers make all their drawings to a 
scale." 
The size of the house having been de- 
cided upon, it was determined to com- 
mence operations at once, so Fred chose 
out a number of boards, and under the 
directions of his father measured off the 
stuff. 
For the sides he took boards ten inches 
wide, and cut them off 27 inches long. 
These were intended to stand on their 
ends, forming a wall 27 inches high by 
18 inches wide. He planed and jointed this 
stuff, and then matched or tongued and 
groved the central joint with a pair of 
match planes* his fatiier went out and 
bought, whilst he was cutting the stuff. 
*Fig. 22 shows a pair of match planes in position 
for work, s s s s shows the several pieces of 
stuff tongued and groved. The planes are made 
in pairs, and the irons are nicely adjusted to 
match each other. They should never be used on 
stuff thicker than the width of the grovingiron. 
Different thicknesses of stuff require different 
sizes of planes. 
I Fred then tried his hand at matching 
: the side boards, and soon found that there 
I was no difficulty in performing this opera- 
tion. He finished this work and drove 
i the boards together, then put them aside 
I and began to cut up the stuff for the back, 
' top, and two floors. He made the back 
40 X 27 inches. This w^as two inches larger 
Fig. 22. 
than the floors, as it had to be nailed to 
the sides. The floors we're made 18 x 38 
inches, and each floor was jointed and 
matched and cut square on the ends ; they 
were intended to fit inside the sides, but 
the top, which was left two inches longer 
than the floors, was intended to nail right 
on the top of the sides; it was also one 
inch wider than the floors, because it had 
to be nailed on to the back. 
The back, like the sides, floor and top, 
was made of narrow stuff jointed and 
matched. The two sides and two floors 
were cut to exact lengths as mentioned 
above, and made exactly eighteen inches 
wide. 
All was now ready to nail together, but 
as it was getting late, this operation was 
posti)oned until another evening. 
( To he continued.) 
Home-made Telescopes and Micro- 
scopes.— XIIL 
FORMULA FOR A QUARTER INCH AND ONE 
INCH OBJECTIVE, BY MR. SWIFT. 
^HE following is a very good formula 
for a quarter inch objective of eighty- 
I five degrees of aperture, the radii of the 
I curves being given : 
I 1. Back triple combination. Curve of 
I back surface of crown lens, '525. Contact 
surface, '225. Contact surface of lower 
crown lens, 1*500. Incident surface, '59. 
