Liberty advocate. [volume] (Liberty, Miss.) 1835-1866, 1846-06-27

lluu tDe distance between TWO trees, "A and
, b, which could not be directly measured /
| because of pool which occupied the in
) termedlate space, the distance Of third
point, G, from each was measured, viz
: e A=588 feet and G B=672 feet, an
also The contained angle ACB=55 ded
~ minutes: required the distance A b
lie seized his slate, covered it with
group of figures, performed some OF II
mentally, and brought out the answer il
two minutes, saying $500, 1857 feet"
then gave him this in the mensuration {.
surfaces: What is the area of a trapezol&
whose parallel sides are $50 and 1928
and the altitude l540l He walked rapid
j ly across the floor, and whirled about ID
and fro and replied, "l52,075." Thels
said |, if the diameter Of the earth be-
1921, what is the circumference lld
said, instantly, "248,846, 1856" To d.
this, he multiplied 1921 by 3,t46. This
he did mentally quicker than | could
write the answer. Then gave him this
How many acres in a circular piece OF
ground whose circumference is 3l,4l6.
miles? He sprung on to his feet, flew.
round the room, and. in a minute saldJ
I"50,2656. Then said |, Required the
number Of acres Of blue sky in an eclipse
whose semi-axes are 80 and % miles,!
He began to walk the floor again, twisting
bis lutte body, and whrlng his eyes
i spasmodically, and in about minute
said, 81, 759, 1896 acres" How did you do ii?
said |. Said he, "Mutipy the semi-axesI
, together, and that product by STAG and
that product by Gao" And did you per-
n form the entire operation in your mind sol
soon2 "Yes, sir.n Then took him into
the mensdraton of solids. Said |, What
is the entire surface Of a regular pyramid
/ whose slant height is seventeen feet, and
the base pentagon, of which each side
is 33 5 feet? In about two minutes, alter
q amply!ylug round the room, as his Gus
! tom is, he replied 1886, 1868" How
did you do it? said |. lie answered,
"Multiply 1876 by 5, and that product by
> 8,5, and, add this productto the product
: obtained by squaring 1915, and multiply
ing the square by the tabular area taken
a from the table corresponding TO penta-
gon." On looking at this process, II !:
!. lstsiotly scientific. Add 10 his the fact
! that | was examining him on different
branches Of mathematics, requiring the
! application Of different rules, and that ne
! went from one sum to another with ra
\ pldity, performing the work IN his mind
: when asked to, and the wonder is sill
/ greater. Then desired him TO find the
= surface Of sphere. Hence, said |, Re
, CURED the area of the surface OF the
earth, its diameter being 1921 miles? lie
i, replied as quick as thought, "l97,lll,024
. square miles," To do it, he had to square
! 1921 and multiply the product by 3,l4l6
t Then I wished TO give him the soldity
d of a sphere; therefore, said |, What is
n the soIidty Of the earth, the mean d.
, ameter being 1887 miles! He wri-
t lhed about, flew rapidly ABOUT the room,
r flashed his eyes, and in about a mi
mute said, "259,992, 792,083." To do
| this, he multiplied the cube Of 1887 BY
E 5236. believe he used few figures in
2 doing this sum; but it was not necessary,
, as he performed much larger one in his
mind, as shall soon show. The next
: sum gave him was this: How many
$ rails will it require to fence a circular
' field, SO that there shall be as many acres
/, the field as there are rails round 1.-THE
, fence being five rails ten feet long, or
e Iaving ten feet on the circumference?
S "O!n said he, 81 guess | cant do it," 80!
. yes cam" said he, leaping on TO the floor
!, and hurryng about the room; and IN
d about two minutes after he put hiss mind
e upon it, he said, at will take 36,848,096
b rails" The mode Of doing this was IN
! genious, aud shows his power Of compre-
) bending not only the nature ola sum, but
I also the mode Of performifgit On ask
ing him to explain how he wrought II, he
! replied, "lf five rails fence Ten feet Of the
J circumference, one rail will fence two
eet; then shall have fenced piece of
ground TWO feet at the circumference and
) at the centre. But by dividing this in
the centre and reversing the ends II will
/, be one foot wide. Now how far must this
f.; strip of land extend to make an acreg
Multiply 100 by Ia and twill give the
I square feet in an acre, which is 1850.
; This is the radius o! the circle. Twice
: this is the diameter mul tipIled by 3,l4l6l
gives the feet in the circumference, and
) that product, divided by 2, gives the mum
Der of rails and the number Of acres. Or,
which is the same thing, as Is both a
, Imutipher and a divisor, neglect Doth
steps, and the radius, multiplied by3, l4l0'
t gives The answer" Now let 1t be re-
I nembered that the boy is only ten gears
!. old-that he did this sum for the prs
time in about tDo minutes, almost wholly
lin his head--and who can account for ltF
Then asked him about his rule respect