The Sun.
London, England, 1839-05-30 00:00:00

THE SUN, LONDON, THURSTIAY, MAY 3Q 1839,

locities,

ATMOSPHEAW PRESSURE AS A
LOCOMOTIVE POWER 0 laLROA-DS.:

TO THE EDITOR OF THE SUN.

Star—An etropeoug statement, which may prove in-
litifotil bating dppeared in your yesterday's Even-
ing Sou'enal, I address you ft, request the favour of your
insetting the follow/lilt-6e eoffeCtion of that error.
Undei tte title quoted above you observe that—
" Several p9tins hive been proleeed for propelling car-
riages on railroads by ainYo'splictic pressure; hitherto, how-
ever, without success. The i7.ftt these was Mr. Val-
origjpal notion of shooting 6: r*vsengers from
London to BrlgVen inside a large pipe, exhath.ie'd of air
by a pump at tl4e other elttrernity. One disadvaniMe of
this project, which probably did 65! oe.)qur to the inventot,
was, that unless the distance was certain 61 king accoro-
p!ished within three minutes, all the passengers'e4r444 be
dead from want of air before they arrived at their det-
ti n a ti on. "

That this impossible and shocking velocity of 1,000
miles an hour should be thus adverted to, after I hail,
in my first publication on the subject 14 years ago, repu-
diated it in the following words, was certainly not ne-
cessary :

" It is well-known that air will rush into a vacuum
at the rate of nearly 1,000 miles an hour. Now, although
it is no more expected we should be conveyed at any such
rate as that, than it is intended we should be placed
in a vacuum, yet are, both this almost inconceivable velocity,
and what is generally understood by the word vacuum,'
so connected with the subject under consideration, that it
becomes unavoidable to advert to them, injurious ay they
must prove, and strongly as they will array our precon-
ceived notions and prejudices against the proposition."
" Talk of air-pumps, and the idea of a vacuum becomes
conjured up. Once conceive that it is proposed to produce
a vacuum in a tunnel many miles long, and'a prejudice
is excited which no after arguments will remove,
so evident is the absurdity of the misconceived
proposition; and so is the effect which it is intended to
produce (1. e. a diminution of density and elasticity inside
the tunnel), mixed up with, and mystified by this 'vacuous'
idea, that judgment becomes dealt out by coup de main,
and proposition and proposer are swept away and consigned
to the contempt they are deemed to deserve."
" The degree to which air would be exhausted from
the tunnel, might scarcely ever be sufficient to sink
the barometer two inches lower than one exposed
to the atmospheric stood at; so that even were we
exposed to this degree of vacuum,' no inconvenience
would be felt. But we never shall be exposed to it, any
more than those who witness the cruel experiment of put-
ting a mouse under the receiver of an air-pump, and then
exhausting it, are exposed to what the little animal suffers.
Between those who see, and the poor creature which feels
the effect of the apparatus, is the side of the receiver. And
between the part of the tunnel in which the exhaustion (or
rather the difference of density) is, and the passengers in
the vehicle, would be the end of the vehicle; so that,
though close to them would be an atmosphere rarer than
(we will suppose) it might prove pleasant to be in, yet
would the atmosphere they actually were in be the same as
that of the air at large."
In another publication, six years ago, was the follow-
ing paragraph :
" When the Brighton Committee rode in that tunnel,
one of them brought with him a mountain barometer, that
he might ascertain the degree of ' vacuum' or exhaustion
necessary to move the carriage. This barometer was ac-
cordingly suspended in the part where the vacuum' was
to be produced, and the vernier adjusted with the
greatest accuracy. But to his surprise the degree of
exhaustion was not sufficient to lower the baro-
meter in the least degree. Being aware of this, I
had spirit guages previously prepared, one of which was
fixed in the end of the carriage. But even this guagel
though nearly fifteen times more sensitive than the barome-
ter, was affected hardly enough to be visible, the amount
of ' vacuum' indicated by it, being only about ten grains
per square inch, or less than the ten-thousandth part of
a vacuum."

These quotations may, perhaps, be sufficient to show
that my proposition was not absurd, as your yesterday's
observations thereon must cause it to be considered.
But as no one beside myself knows how truly valuable
the principle is, I beg leave, in justice to that by
which I mean to stand or fall, to observe, that it was
the man who failed, not the thing; the individual,
not the principle ; that failure, however, being
caused by parties whose conduct I could no more
anticipate and guard against, than the late Mr. Perce-
val could against the pistol of Bellingham ; though,
should life and power be granted me, I will as surely
remedy it, as the sailor remedies the deviations from his
course which adverse winds occasion.
You appear to consider Messrs. Pinker's and Clegg's
methods of applying the pressure of the atmosphere
superior to mine. Would you do me the favour of read-
ing pages 31, et ceq., of the (as yet unpublished)
pamphlet accompanying this, it is . possible you may
change your opinion relative to the former gentleman's
plan ; while I beg leave to observe as follows with re-
spect to the latter :

In the circular which Mr. Clegg's engineers, sent to
some of the papers, it is stated (as in that you quoted
from yesterday) that " an available tractive force of
7141bs is thus obtained, which will draw a train weighing
13 tons upon an inclined plain of one foot in fifty ; and
with engines of the above power (from six to twenty-
five horses) the trains can be impelled at the rate of
thirty-five miles per hour." The under-attached table
from a yet incomplete sheet of the pamphlet mentioned
above, may, possibly, cause you to perceive that your
observation, " one disadvantage of this project, which,
probably did not occur to the inventor" will more justly
apply to others, than to me. Soliciting your insertion of
this, I have the honour to remain, Sir,
Your most obedient servant,
JOHN. VALLANCE.

That famed locomotive engine the Planet, exposed
nearly thirty-five square feet of surface, at right angles
with the air it passed through. Others of above twice
her power having since been made, and it being probable
that they will be made still larger, it may be none too
much to assume that they will expose forty square feet
of surface. The resistance of air to bodies passing
through it, being at the rate of twenty miles an hour,
equal (speaking roundly) to two pounds per square foot
of flat surface, and that resistance increasing according to
the square of the velocity, the resistance it opposes at
high velocities will be (roundly) according to the following
table

Which resist-
anccs having to
be overcome at
the rates of the
first stated num-
ber of feet per

second, require
Locomotive engines, Experience resistances power equal to
(drawing no load) mo_ from that air, equal that of the un-
ving through still air, (roundly) to the understated num-
at the under-stated ye- der stated number of ber of horses, to
pounds. overcome them
Per On 40
Feet per Miles per square square
second. hour.
.foot. feet,
14.666 lO 0
29.332 2O 2.

0

4
44.
58.660
73.333 ::,0 12.5
88.
117.328 BO 32.0 l2BO 270
146.666 100 50.0 2OOO 528
176. l2O 72.0 ... —2BBO 912
Now as a velocity of 40 miles an hour requires power
nearly equal to that of the largest locomotives which have
yet been made, and as Dr. Hutton found that giving the
moving body a point in the shape of a cone, the height of
which was equal to the diameter of its base, diminished
the resistance of the air only half, therehence (and with-
out adverting to the additional resistance which must be
created by the tenders of, and trains drawn by the engines)
arises a very sufficient explanation why no greater velocity
has been attained by the (nearly) ten times more powerful
locomotive engines now made, than was first attained by
those which ran at the rate of 35 miles an hour on the
Liverpool and Manchester Railway in October 1829.
E

DINBURGII AND GLASGOW RAILWAY.—
Upwards of 20 miles of this line aro contracted for, and
eight miles more are advertised. These 28 miles compre-
hend all the heaviest, and, consequently, all the most te-
dious works ; thus putting it in the power of the Directors
to regulate the letting of the remaining contracts so as to
secure the completion of the whole line about the same
time. The contractors are taken bound to finish their
work in 1841, and from the well-known energy and skill
of some of them, there is little doubt of the line being
opened about the time expected. Messrs. Gibb and Son,
by the erection of an extensive viaduct across the Almond
Valley, are now exhibiting to the traveller between
Glasgow and Edinburgh, the nature of the line
along which he will hereafter be conveyed to the me-
tropolis of Scotland. Messrs. Marshall are busy at the
Glasgow terminus, and arc burrowing in the earth
at various places to facilitate the execution of the tunnel.
Messrs. Forbes, Ross, and Mitchell, are also making con-
siderable progress with the tunnel through Callender
Park ; and the other contractors are either progressing sa-
tisfactorily, or big with the note of preparation. The Di-
rectors are much occupied with arrangements for the land,
and have made several satisfactory agreements. They have
settled with the Union Canal Company on terms ac-
ceptable to both parties, and the Forth and Clyde Canal
Company have permitted the line to pass under their Ca-
nal without any equivalent. These two Companies were
the most determined Parliamentary opponents which the
Railway Bill experienced, and it is pleasing to perceive
hostile feeling give place to amicable intercourse, and to
the satisfactory adjustment of the interest of parties.—
Edinburgh Courant.
RAILWAY COMMUNICATION BETWEEN
LEEDS AND YORK.—Next Thursday, the 30th instant, that
portion of the York and North Midland Railway, which
effects a junction between the Leeds and Selby Railway
(near South Milford) and the city of York, will be opened
for the conveyance of passengers ; and thus there will be
a Railway communication the whole distance from Leeds
to York. The distance by Railway wilt then be 27 miles,
and the trains are expected to travel it in the space of an
hour and a quarter.
A LITERAL ANSWER.—Rather a laughable
circumstance occurred in our Justiciary Court on Monday
week. In a case of house-breaking, a female, among
other witnesses, was called, who keeps a humble lodging..
house in Gatehouse. After administering the usual oath,
the Judge (Lord Mackenzie) inquired in common form
whether she had received, or been promised anything for
her evidence. To this question the woman answered
" Yes," and when the wondering Judge inquired what,
she answered with the greatest naivete—•'a summons."
This eon and simple reply, set the Court in a roar, in
which th Judge good-naturedly joined, at least for a mo-
ment.—Dumfries courier,