DIS8 
vi 4.69. § Stem with two leaves and one flower. 
Sp. PL 
Germen nero 
as braGtea.”? Native of the . Dy. fecunda. 
poe ecw Thunb. Prod. 3. TO circumflexa ; 
Lion. Sp. Pl. 1344.) ‘ Stem with two lincar leaves, and 
many flowers eee ne way.”? This grows alfo at the 
Ca € 
ee veils and poe twifted appendages are very confpi- 
cuous. 5. D. cordata. Swartz. Orchid. 41. Willd. 60. 
ties with two le pond ee: {mooth leaves, and many fe- 
rate flowe he ifland of Mauritius. 
aes lot, ay or "Bve a a fort oe corymbus, with 
an ovate bra o each. hefe we are enabled to add 
a non-defcript tae pboftifolia, « Srem with two 
oppofite ovate {mooth leaves, anal feveral bra€teated ar rers.! 
Native of the fle de Bourbon, communicated by aaa 
from the Linnzan herbarium. oot tuberous. ae ipa 
high. Leaves abuve an inch lony, oppolite, a out the mid 
dle of the ftem, fpreading, obfcu rely five-ribbed. Powers 
three or four in a braéteated fpike, yellowih. Bradcas ¢l- 
liptical. 
DISPERSE, in scot Language. To difperfe a body 
at of an engagement, and to rally them, fo 
purfuit, 
¢ 
4 
with well difciplined troops, r 
the ay to igs ae Id i ihewile be communicated te erery 
r to ah eive the enemy more eficCtually, 
m in his entrenchments with great 
fhew of vigor, and in fe eee of the conflict to beat the 
retreat ; on this the affailants fhould retire in feemin ng dif. 
order, but with (tudied atcention to the o r If 
incividt 
n be 
r ee aie behind which fom 
could be placed in the effect wili be confiderably 
encreafed ; ‘both ia encrealng the furprize, and panic, and 
wo fa It ought, howevei: 
t when once foldiers turn 
the pro 
BG rifle-men, and otherlight co 
ISPERSION eins in n Opi notes the enlarge- 
ment of a pene or beam of ht ne is produced by its 
pzflage from one medium into a aie and this enlargement 
lum, 
tion of the prefent ee 
point out the diftin 
When a beam of light, (fuch, for ae as ane eds from 
a hoie in a window 
of pa- 
the other fide of, and ie a lit- 
the luminous {pot, which is 
neceffarily forms an {pot upon the la 
w this enlargement, being the efe& of the peculiar 
u. XI, 
inclined direétion 
the 
DIS 
figure of the Jens, is not confidered under the prefent ar- 
= 
i 
When a beam of light apa not ina oo hi 
in an oblique direGtion fom one medium into anoth 
dium of a different nature, fuch as fi 
ent 
eee eae: but : slides it g e be 
light is {pread in a fe€toral fo nee and 1 vivid. “ easaeed 
ftripes (fee the articles Licur and ie Now 
this {preading, which feems to arife f ae ee of the 
et is called the difperfion, or cfipatie, oo and is 
the our eae confider wing 
iateaton will re the nature of on ore € evil a 
Plate iV. ‘Opie, jig. 7.) reprefenc a imal! beam of 
the fun’s sizht, which paffes through te tube 1, ard falis ob- 
liquely at C, upon the furfac , of th eaten ue medium 
e it water, or ait or other tranfparent fubftance. 
Let a bie cf any diameter be drawn round the centre C, 
cutting the beam of light at O. the perpendicular 
N throuzh C. 7 he beam of light, by its falling obliquely 
upon the fares ce the water at C, will be refratted, vz. 
will be bent, from i its ftraight dircétion © P, into the more 
s, and will at the fame time be fprea 
into { C ¢. which is are the difperfion of 
the livht. This fe€tor r Cz is itfelf divided into {malier 
{-Ctora of different colours; viz. next to ie upper line Cr, 
the colour 1s red, and thence the light gradually degene- 
rates into orange, yel’ ow, green, otue, indigo, and violet, 
which is neareft to the lower boundary this may 
ag a white farface at the bottom of, or 
. 
fa 
cor 
Spd 
mens 
om 
et perpendiculars be 
Peis on ae ae El va Gen ce hie is drawn through 
the middle of the angle Ch, is ean direGion of the 
refracted light, and s ¢ is its iat or ee of the mean angle 
of refraction ; OM being the fine of the angle of incidence, 
rw and #y are the fines of the extremes, ot which ¢ g is che 
fine of the Me age colour, and r w the fine of the leujl 
refi a colo 
foun d, that through the fame medium, the 
rel of dipedion§ is peek proportionate to the mean os 
refraction, and, o ourfe, when the: mea ale of 
fedion is = {m 
CM, and i aa the meaa angle of refra€tion sC N, 
are confiderably Jarger; then the angle rCé of difperfion 
will — be large enough to exhibit the above- neat! co- 
Jour 
Di ent refractive media have different difperfive powers ; 
or sane, the angle of posi OCH, femain ing the 
fame, = on ae the mean Sa refra€tiou.s CN will va 
IDG is water, oF 
perfion is fmaller : in other re Sia ore co mean ae 
> 
power of a given fubilance will not enable us to determine 
its oe es and wice wv rif. 
made the important difcovery of the 
rT aa ae ogibiliy of the rays of light, which convetted 
the white folar light into the colours of the rainbow, when 
that light was de to pafs obliquely from one tranfparent 
medium into another, had not. the lecft fufpicion ofthe 
5D duterent 
