1800.] Sixty Articles of Literary and Philofiphical Intelligence. 347 
private fubfcription thus fupply a great 
defideratum, the want of which has long 
appeared, in the eyes of foreigners, a fig- 
nal difgrace to the metropolis of Great 
Britain. 
It is not generally known in England, 
that the profeffion of the Barbs has not 
yet gone into difafe in the Highlands of 
Scotland. Thefe bards are to be found 
only among thofe who have little know- 
Jedge of any but the Gaelic language and 
its ancient fongs. Some of them are of 
the female fex. They pour out their 
verfe aimoft without premeditation, and on 
any fubje&t that may be occafionally pre- 
fented, and greatly refemble, in .poetical 
‘ability the Italian Improvifatori. Ar- 
gylefhire, Peiththire, Rofsthire, Invernefs- 
fhire, and the Tile of Sky, are the diftriés 
in which they are chiefly to be met with. 
An ingenious’ gentleman of London, 
has lately, by a repetition of the experi- 
ments of fir Ifaac Newton concerning 
light and colours, afcertainéd, ‘* that pri- 
migenial light is white; and that the feven 
different colours which appear in the prifm 
are produced by the inflections and changes 
which the white ray undergces in pafling 
between painted furfaces, and through 
tranfparent media.”’ 
Having, in a former number, announced 
the important difcoveries of Dr. Her- 
SCHELL, on the different temperatures of 
the pritmatic colours, we fhall now give a 
fhort abitra& of the two interefting papers 
on this fubjeét, which have been laid be- 
fore the Royal Society,—Being engaged 
in a courfe of experiments to afcertain the 
beft method of viewing the fun with large 
telefcopes, Dr. H. made ufe of vaiious 
combinations of differently coloured 
glaffes, for the purpofe of darkening the 
image of the fun. While ufing thefe, he 
remarked that feme which tranfmitied 
little light excited a {trong (er fation of heat, 
while others that allowed a freer paffage 
to the lirht appeared to tranfmit but little 
heat. Now, as in thefe different combi- 
nations of clafles the fun’s image appeared 
differently coloured, he was induced to 
f{uppofe that the prifmatic rays might dif- 
fer from each other in their power of heat- 
ing bodies. To afcertain this, a ray of 
the fun was divided by a prifm, into a 
fpeétrum, and the different colours ap- 
plied fucceffively to the blackened bulbs of 
two thermometers, the experiment being 
made repeatedly, and always with a fimi- 
Jar refuit, it appeared that any of the 
prifmatic rays falling on a body will in- 
creafe its temperature, but that this effect. 
/ 
is inverfe'y as their refrangibility, the 
leaft increafe being produced by violet, 
and the moft by red rays. Where the ad- 
ditional temperature occafioned by violet 
rays is equal tor, that of green is equal 
to 14, and of red equal to34, Thus far 
being afcertained, it became an objett of 
importance to determine whether the z//z- 
minating power of the prifmatic rays co- 
incided with the order of their calorific 
powers. With this view a number of ex- 
periments were made, agrecing unufually 
well with each other, and concurring in 
the conclufion, that the maximum of ilu- 
mination lies between the brighteft yellow 
and the paleft green, that the red rays af- 
ford lefs light than the orange, and this 
laft Jefs than the yellow; that the green 
itfelf is nearly as bright as the yellow, 
that the blue is upon a par with the red, 
the indigo is much lefs than the blue, and 
the violet is by far the faintett of all. 
Having thus afcertained than the heat as 
well as light of the folar rays is refran- 
gible, but that the place of greateft illu- 
mination is about the middle of the fpec= 
trum, whereas the heat goes on increafing 
from the violet to the red; the queftion 
naturally arofe, whether the rays of heat 
might not be fo far feparat-d from thofe of 
light by their different degrees of refran- 
gibility, as that fome of them fhould 
actually fall fome diftance beyond the ca- 
loured fpeétrum on the red fide. For this 
purpofe the fpectrum from a prifm, 52 
inches diftant, was thrown on a ftand co- 
vered with white paper, and it was found 
that rays affording no illumination, at the 
diftance of half an inch beyond the ex- 
treme boundary of the red colour, raifed 
the thermometer 64 degrees in ten mi- 
nutes: that thofe an inch beyond the red 
produced a heat of 53 degrees in thirteen 
minutes, and thofe an inch and a haf be. 
yond the red produced 3% degrees in ten 
minutes. At the other extremity of the 
{pcétrum there was ro increafe of heat be- 
yond the boundary of the violet rays. As 
in thefe experiments the limits of heat ex- 
tended beyond thefe of ilumination on the 
red fide, it became of importance to deter- 
mine the place of the greateft calorific 
power. This maximum of heat was found 
by experiment to be about half an inch dif- 
tant from the boundary of the red colour, 
and the heat at oneinch was equal to that 
of the middle of the red colour itfelf, The 
boundaries of the calorific/pedtrum ite be- 
tween the extreme of violet and an unde- 
termined point, at leal 12 inch beyend the 
red colour, From the above very important 
Yy 2 facte 
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