174  Obfervations on Platina, 
of the ftar, without intercepting, by the head, the rays which 
proceed from it. 
In the beginning of the year 1791, Trudaine entraitéd to 
me the telefeope which he had procured at London. -Aftro- 
nomy is indebted to Herfchel for the nobleft difcoveries of 
this century. Thename of that obferver will be tranfmitted 
tothe moft diftant ages. He has augmented our planetary 
fyftem, and enriched it with a new planet, accompanied 
with feveral fatellites. In 1671, Dominic Caffini, obferving 
the moon with an excellent telefcope of Campani, remarked, 
in'the obfcure part of her, fome fmall whitifh nebule. This 
imterefting phenomenon did not efcape the telefcopes of Her- 
fchel; and after the year 1784, that able aftronomer an- 
nounced, that he had feen a burning volcano in the middle 
of the fpot called Ariffarchus. We find in the Memoirs of 
the Academy of Sciences for the year 1706 the following re- ° 
matkable paflage of De Ja Hire: ‘ The fmall fpot of Arif- 
tarchus ‘is fo brilliant, that fome have believed it to be a 
volcano.” 
Are thefe fmall whitith nebulz bodies luminous of them-+ 
felves, or do they enjoy only a borrowed light? Such is the 
queftion which I propofed to refolve, by affiduoufly obferving 
thefe fmall nebule, both with Herfchel’s telefcope, and that 
which I caufed to be conftruéted of platina in the courfe of 
the year 1791, on the model of that of the above aftronomer. 
Being deprived, fince September 1792, of the ufe of that 
‘inftrument*, the conftru€tion of which had coft me great 
* Tele{copes of ftill greater magnifying powers might be fo eafily procured 
iat Paris, ; that thofe who are truly interefted in the progrefs of the arts 
_and {ciences are not a little aftonithed that the great telefcope of fixty feet, 
announced in all our journals, is ftill a project; and that no one even fo 
much as thinks of realifing it. Though the art of making large fpecula 
“is attended with fome dificulties, it however requires neither the fame 
talents rior the fame patience as that of conftruting large achromatic ob. 
ject glaffes. The catoptric telefcope requires only the regular lahour of a 
fivgle furface, and it is the work of a few moments which forms or cal 
the polifh of the concave furface of a large fpeculum. 
labour 
