744

AMERICAN RAILROAD Jon1tNA.IJ. AND

3-’

iinient. The advantages possessed by the

mouth blow pipe over all those instru-

T meats whose blast is produced by artifi.

cial moans, consists in its portability,
economy, and the facility of immediately
suspending or modifying the blast. “The
chemist does not possess,” says Dr. Fara-
day, “a more ready, powerful, and gene-
rally useful instrument, than the mouth
blow pipe, and every student should early
accustom himself to its effectual use and
application.”

:-

€33

" visible. The pupil will now he possessed
lof a blow pipe (fig. 3,) with an exceed-
ingly minute jet; and if he puff out his
checks to the utmost, and place the end
I) within his lips, while the other extremity
is held within a short distance of a can-
dle, (fig. 5,) he will, after a few trials,
find no difficulty in keeping the flame
coiztimmlly, and without 2'11termi.§sion, hori-
zontal and clear. The operation which
he will be required to perform, in order
to keep his cheeks constantly distended,
notwithstanding the esca.pe from the jet,
cannot easily be described, but will na-
turally ofi"er itself when the expenditure
of air is very small. When the pupil has
succeeded in keeping up a constant blast
for several minutes, by this means, he
may enlarge the aperture by degrees,
practising between each enlargcinciit, till
he finds he can manage a blow pipe with
a large here, when he should purchase

 

 

B

r°r°

The supply of a continued stream of
air, is the chief. dificulty which a begin-
ner experiences in learning the use of
this instruiiieiit,aiid this difficulty is, I ap-

, prehend, not unfrequently increased by
the employment of a blow pipe with too
large an orifice, in the first instance." The
following method of constructing, will, I
havereason to believe, he found more of-
iicacious than an other hitherto publish.
‘ed: 511103 I MY _. by its means, succeed-
‘efli it} less than half an hour, in commu-
nicating the art of blowing to a class of
several persons. Let the pupil procure
a tube of glass, 1) 6, about thirteen inches
long, and of the size and thickness of a.
Let him now thoroughly heat the tube at
c, about two inches from the end, by slow.
Hy turp'ing it round in the flame of a can.
die: 6!‘, What is better, a spirit lamp.
When he finds that it will yield, let him
bend it gradually till it has acquired the
positioii represented by fig. 2. The part
at is now to be heated in the same man_
tier, till it is found soft enough to draw
out, when the part is must be gradually
withdrawn, as represented in fig, 4 up it

terminates in a point- this 0'5; ’h
be h Id f _ 3‘ p_ in S onld
e or a iiiintito or-. two m the pomt
Of the ~flt1l'1]t'~}, In Qyigign to thicken ii, and
222°“ cold ‘t ‘S 39. 19.9. grmind away with a.
7

until thug.‘  .poss,i_b’l,e orifice is

one of brass, with an ivory or tinned
mouth piece, for general use.

_ Among the numerous hydrostatic blow
pipes which have already appearetl in
your Magazine, the pupil who wishes to
manufacture his own apparatus, may as.
suredly find one which will form a siibsti-
iute for the table blow pipe. I subjoin a
ll . plan for one, which

~ may be constructed,
at a trifling expense,
by almost every stu.
dent, and in situations
¢ where the articles

,_.of wo1'kniaiisliip re-
 quisite for the con.

struction of a more

complicated machine,
could not be procured.

a 5 (fig. 6,) is a com-
mon pail, about half filled with water; c
s a large flower pot, inserted, and fasten-
ed in by any convenient method ; cl is a
mouth blow pipe, (glass would do on an
emergency,) fastened in air tight, with a
cork and lute, to the hole at the bottom
of the flower pot; e is a bent tube of
glass, or metal, terminating under the
mouth of the flower pot. When air is
blown in from the mouth at 6, it rises into
the body of the internal vessel, and dis-
places the water, which, in endeavoring
to regain its level, forces out the air from
the jet ofthe. blow pipe, with a force pro-

6.

  
 

water displaced.

On. the Resistance of Fluids; by Geo. VV.
KEELY: Professor of Natural Philoso-
phy, in Waterville College.

s1R.-I perceive in No. 55 of the Journal,
that Professor Wallace has announced it
new measure of the resistance of a fluid in
a direction perpendicular to a plain surface
moving in it, viz: That it. is as the sine
of the inclination of the plane. T Permit me
to statemy reasons for adhering to the old
doctrine, that the perpendicular resistance
is as the square of the sine of inclination.
It is well known that the latter measure has
been deduced from the allegetl facts that
the number and the force of the resisting
particles vary as the sine of the inclination.
If it be t1‘t1e that the res_,is_t;i=,nco' to a plane

portioned to the height of the column of ‘

surface moving in a fluid is as the number
of particles it strikes in its course, and that
the number of particles in any indefinitely
thin fluid lamina is as the area of that
lamina, (nei-
ther of which

A . we think Pro-
\_ ' fessor W. will

‘\ deny,) it fol-

\ lows that, if
C‘ -.............. 1) BD be a sec-
tion of it

E F plane inclin-

ed to the di.
rection BA of its motion, and BF an equal
section of an equal plane perpendicular to
the same direction, the number of particles
BD will strike is to the number that BF will
strike in’ the same. time, as the parallelo-
gram ABCD is to the parallelogram AEFB_ ;
and the resistances are therefore, on this‘
account, as B6} is to BD, or as the siiies ot
the inclinations of the sections; the resist-
ances to the planes are of courSe 111 the

same ratio.

Now this familiar demonst.rat.ion 'v'volil(l
seem to settle the question ; but Professor
Wallace nrguics, “ that the ‘nijmbcfr of pat‘-
ticles striking the plane. does not depend on
the breadth of the fluid column BG BF, but
on l]l€.S1l’l:f(l‘C8 of the plane, beeau‘~e the
particles that act on the plane are those in
contact with it, and tlierefore'. their tllll’lli3t‘.i‘
is as its superficial area.” Now, admitting
it to be true that the number of material
particles in contact. with the plane, at any
instant, is t.1ie.same, whctlicr it he perpen-
dicular or inclined to-the direction of the
motion, it does not, we think, necessarily
follow that the ntiinbei‘ of particles struck
in any given time will he the same. But
neither is it evident that the number of par-
ticles in coiitact with the plane is the same
for every inclination of the plane. The
burden of proof, however, seems to lie with
Prof. W. He‘ has assumed the general phy-
sical fact that the number of particles iii
contact with the plane, at any instant, is
the same for any position of the plane, and
he has deduced an inference, not formally
expressed, indeed, but surely implied, other-
wise the argument is worth nothing, that
the number of particles struck in any given
time is as the number in contact with the
plane at any instant. Now we think the
fact and conclusion may very safely be de.
mod, and it becomes Prof. W. to show that
they are consistent with some hypothesis
respecting the form and relative position of
the ultimate particles of a fluid body. In
any hypothesis, we believe the following
positions will be found to hold :

First. Whether the number of particles,
at any instant, in contact with the plane, in
different positions, is the sonic, depends
wholly on the hypothesis.

Second. If the number is the same in
difl"erent positions, it will be found that the
number of fluid strata struck in any given
time, is as the sine of the inclination.

Third. If the number is not the same,
then it varies as the sine of the inclination.
and the number of strata struck will, in any
given time, be the same.

If Prof. W. can devise any hypothesis
with which these positions do not agree, we
will allow he can disturb our belief in the
truth of the law of the square of the Sines‘

The wide difl'ercnce between the results
of observation and those of the old theory.
would tend rather to dissuade us from ad-
mitting the truth of the new, when we con-

‘ sidcr what important physical circuinstaii-

cos are and must. be omitted in the condi-

tions.--.-[S3jillinian’s J.ournal.]