AN ATMOSPHERIC ENGINE. 
331 
ITien follows a botanical account of the 
tree Hevea, from which the juice is obtain- 
ed. 
While the processes suggested in this paper 
are in some instances not very dissimilar to 
those since employed, in others they are to- 
tally unlike, and have been found utterly 
useless. The principal scheme was to cover 
woven fabrics with a film of caoutchouc. 
To this there were insuperable objections. 
No substance was then known, which, 
while capable of dissolving solid caout- 
chouc, was cheap enough for popular use. 
Besides, when managed by any process then 
known, it was left on the surface of the 
cloth in too viscid and adhesive a state 
to be at all serviceable. The only hope, 
therefore, was, that the juice might be ob- 
tained and applied in its native fluid state, 
the solid caoutchouc settling upon, and ad- 
hering to, the substance to be coated. With 
how little success this attempt was attended 
will be seen hereafter. 
It was, however, in the same year (1791) 
thatthe first successful trial was made ; but it 
was conducted on a different principle, and 
its results, though useful, were very limited. 
The following extract shows the mode of ope- 
ration adopted by Mr. Grossart, as explained 
by him to the Academy of Dijon 
“ It has been remarked, that if shreds of 
these bottles fresh cut down be pressed very 
close upon each other, they may be made 
to adhere so closely as to appear one piece. 
This operation is facilitated if the caoutchouc 
be softened in warm water. Upon this 
principle he thus proceeds ; — After having 
provided a mould of a proper size for the 
open of the tube intended, he slices down 
the caoutchouc into thin shreds, puts these 
into boiling water ; after they have remained 
there for some time to soften, he takes out 
these shreds, and rolls them tightly on the 
mould, taking care to make the edges over- 
lap each other; one shred is applied after 
another, till the mould is aU covered to the 
thickness wanted, then a ribbon is bound as 
tightly as possible over the whole, and above 
that it is still more closely bound by a tire 
of packthread, laid close to each other over 
the whole surface. In this state it is allow- 
ed to remain for some days, when the pack- 
thread is unbound, and the ribbon taken off. 
The mould may then be easily drawn out af- 
ter dipping it a few minutes in hot water, 
and the tube is formed.” — Mechanics'' Ma- 
gazine. 
(To be continued.) 
lift '8 
ATMOSPHERIC-ENGINE AND SELF- 
REGISTERING BAROMETER. 
The following is the description of a ma- 
chine which may be called an atmospheric- 
engine, the motion and effect being produced 
through the variations in the pressure of the 
atmosphere. The power of the engine, as 
will be seen, is rather circumscribed, but still 
it is capable of being made to act with any 
assigned force through a small space. It 
might, perhaps, be useful in any operation 
requiring other machinery to be set in motion 
at a point of time when the barometer indi- 
cated a particular state of the atmosphere. 
It is easily convertible into a self-register- 
ing barometer. 
That part of the accompanying figure in- 
cluded between (o) and the number 30,5, 
represents the sec- 
tion of a tube, closed 
at top and open be- 
low. It is attached 
to the end of a chain, 
by which it is suspen- 
ded, and which pass- 
es over a pulley, the 
other end being fas- 
tened to a fuzee and 
counterpoise, or a 
fuzee and spring- 
barrel. Either will 
be practicable ; but 
we must conceive it 
to be so suspended, 
that it will descend 
through equal spa- 
ces, when it becomes 
charged with equal 
weights. The lower 
(open) end is to be 
placed in a fixed ves- 
sel, represented in 
the figure. This ves- 
selcontains mercury, 
the surface of which 
rises to (o), which 
is above the end of 
the tube, when the 
latter is at its highest 
point of suspension ; it is so represented in 
the figure. The numbers indicate the 
length of the tube, in inches, between the 
points opposite to which they are placed ; 
and, therefore, the whole space included be- 
tween (0) and 30'5 will be 59’8. 
The figure is drawn to represent the 
tube at the height at which it would be sus- 
pended when the column of mercury it is 
supposed to contain stands at 29‘3, being 
just so many inches above (0) the surface of 
the mercury in which the end is immersed ; 
the space in the tube above 29*3 being then a 
Torricellian vacuum. The surface of the 
mercury in the lower vessel is prevented from 
rising or falling from its place at (O) by means 
of a floating-cistern containing mercury, and 
placed in an adjoining vessel, not represented 
in the figure, the communication being main- 
tained by means of a fixed syphon. The 
