i - 
and which will probably always remain 
unknown to us. If the sun alone move, 
we nay im time, and by.accurate ob- 
servations,’-discover this motion with 
~ precision; but if the stars. have also a 
motion, the separation of the unknown 
will be impossible, and hence much 
embarrassment will result to future as- 
tronomers, if the observation should be 
interrupted for some ages, and if, after 
2 period of barbarism astronomers should 
be inclined on the revival of the sciences 
to calculate anew the motions of the 
celéstial bodies, by the comparison of 
their observations with ours. But, even 
-on this supposition, which is happily 
very improbable, it only follows, that 
the observations made during the eigh- 
teenth century would appear a. little 
less precise, which could not, however, 
render them of so little value as the 
very limited number of rude observations 
handed down by the Greeks, have been 
to us. 
The problem of discovering the wheel- 
work necessary to represent the planetary 
motions has been resolved, in the most 
satisfactory’ manner, by M. Hughens, 
by continued fractions which possess the 
advantage of furnishing approximate va- 
~ luations, always expressed by the smallest — 
possible numbers, in the difterent degrees 
of approximation to which we may judge 
proper to carry them. But’this method 
cannot always be adopted by artists, 
who construct orreries. M. Burckhardt 
has therefore pointed out calculations 
more easy and.sufficiently exact for prac- 
ticul purposes. But the most important 
part of his labours, according to M, 
Delambre, consists in the advice which 
he offers them to abstain from all those 
researches which can neither be useful 
to themselves, nor productive of any real 
utility to science. The most perfect 
machine must always represent with less 
precision the notions of the planets than 
the most indifferent ephemeris. An 
artist possessed of ordinary talents can 
only, after a vast expense of labour and 
time, produce a very imperfect work, for 
which it wiil be impossible to find a 
purchaser; but should he even evince 
extraordinary capacity, however we may 
be led to admire the resources of his 
genius aud art, we must still regret, that 
“they have been wasted on such an un- 
productive undertaking, His planeta- 
rium, or orrery, will be at a price above 
the reach of individuals, and governments 
must perceive that they can make a much 
more usetul distribution of the rewards 
i y *<t « 
Proceedings of Learned Societies. 
[Feb. 1, 
appropriated to industry. It cannot then 
be too warmly inculcatéd on artists to 
avoid such ruinous projects, and leave 
thein to the rich amateur, who possessing 
a taste and talents for such employments, 
pursues them merely for bis own amuse- 
ment, without the hope or expectation 
of emolument. Orreries, besides, are 
not well calculated for instruction, as 
they afford- but.a very imperfect repre- 
sentation of the solar system, They 
display very nearly their ditfereut motions 
in proportions to each other, but neither 
exhibit the size nor distances of the 
celestial bodies. All the machinery 
which we conceal, only gives a very 
false idea of the simple means employed 
by nature. 
M. Delambre next proceeds to notice, 
in conformity to the intimation formerly 
given, the-report of the commissioners, 
respecting the most curious and important, 
inventions, which have been presented 
to the Institute by learned foreigners. 
The report of M. Carnot, concerning the 
machine invented by Messrs. Nieps, to 
which they have given the name of 
Pyréolophora, claims the first notice. 
This word is composed of three Greek 
words wv p, fire; AsgAos, Aeolus, or wind ;— 
and ¢égw, I carry. The inventors intend 
byx,this name to: indicate the moving 
powers of the machine, which consist 
of the wind from a beilows, the fire and 
the air suddenly dilated. ; 
Their intention was to produce a ma- 
chine of equal power with a steam-engine, 
and which would not require such a great 
consumption of fuel. 
In order to form some idea how the 
sudden dilatation of the air is produced, ' 
as well as the model of its action, we 
must suppose to ourselves a copper re- 
cipient firmly attached to a horizontal 
table. To one of the sides is fitted a 
tube, through which a mass of air is 
impelled ‘into the recipient. In its course 
this air meets with some particles of 
combustible matter, that it projects upon 
a flame, with which it enters into ignition, 
The inflamed matter penetrating into 
the recipient dilates the air in it with 
great force, which exerts its action against 
its sides, pushing before it a piston, which 
enters into a secowd tube adapted to the 
other side. This piston impels forward 
a column of water, or any other body 
exposed to its action, after which it 
resumes its place, and the machine ree © 
covers its, original position, continuing 
to act successively in,the same manner 
and all these effects are produced in a 
ae 
