430 M Y O 
which account thofe people cannot fee diftindHy unlefs 
the objedt he fituated at a greater diftance from the eye 
than ip required for thofe whole eyes are of a due form. 
The latter require the afliftance of convex glaffes to make 
them fee obiedts diftindtiy ; the former of concave ones. 
Dr. Wells, in a paper on vifion, lately read before the 
Royal Society, maintains that the focal diftance of the 
eye depends chiefly on the contradiability of its mufcles, 
and that the latter is much greater in youth than in per- 
fons of more advanced years. In youth, the eye is capa¬ 
ble of accommodating itfelf to the light, and the diftance 
of external objects; but, in old age, this contradlile 
power of the mufcle ceafes, and the focal diftance of the 
eye becomes fhorter and more fixed to a determinate point. 
The belladonna plant, applied to the eyes, increafes the 
adtion of the ocular mufcles in the young, but not in the 
old fubjects. Hence the dodtor infers that, Ihort fight 
is lefs owing to the prominence of figure of the pupil 
than to the flexibility of the mufcles which diredt it. To 
this dodtrine we cannot fubferibe, fince it would argue 
that, as people advance in years, they mull expedt to be 
ihorter-fighted, which is contrary to every-day’s expe¬ 
rience. 
In the Firft Part of the Phil. Tran ft for 1813, we find 
an interefting paper, entitled “ Obfervations relative to 
the Near and Diftant Sight of different Perfons, by James 
Ware, Efq.” It contains many cafes of near-lighted per¬ 
fons, with forr.e remarkable changes, produced in the 
fight by different caufes, authorizing the following con- 
clufions: 
1. That near-fightednefs is rarely obferved in infants, 
or even in children under ten years of age. It affedts the 
higher claffes of fociety more than the lower ; and the 
instances are few, if any, in which, if the life of concave 
glaffes has been adopted, increafing years have either re¬ 
moved or lefl'ened this imperfedlion. 
2. That, though the ufual effedt of time on perfect eyes 
be that of inducing a necefiity to make ule of convex 
glaffes, in order to fee near objedts diftindtiy; yet fome- 
times, even after the age of fifty, and after convex glaffes 
have been ufed many years for this purpofe, the eyes have 
not only ceafed to derive benefit from them, when look¬ 
ing at near objedts, but they have required concave glaffes 
to enable them to diltinguilh with precifion objedts at a 
diftance. 
3. That, though the caufe of this change be not always 
known, yet fometimes it has been induced by the ufe of 
evacuating remedies, particularly of leeches applied to 
the temples ; and fometimes by looking through a mi- 
crofcope, for a continued length of time, for leveral fuc- 
celfive days. 
4.. That inftances are not uncommon in which perfons 
far advanced in life, (viz. between eighty and ninety,) 
whofe eyes have been accuft-omed for a long time to the 
ufe of deeply-convex glaffes, have ceafed t» derive benefit 
from thefe glalfes, and they have become able, without 
any afliftance, to fee both near and diftant objedts, almolt 
as well as when they were young. Although it be not 
ealy to afeertain the caufe of this amended vifion, it feems 
not improbable that it is occafioned by an abforption of 
part of the vitreous humour; in confequence of which, 
the fides of the eye collaple, and its axis from the cornea 
to the retina is lengthened ; by which alteration the 
length of this axis is brought into the fame proportion to 
the flattened ftate of the cornea, or cryftalline, or both, 
which it had to thefe parts before the alteration took 
place. 
5. There is reafon to believe, that this difeafe is much 
promoted by the ufe of glaffes; and, that if glaffes are 
not employed, it loon wears off and difappears. Hence 
it is much more common among the higher ranks than 
, among the common people. In the regiments of life¬ 
guards, Mr. Ware did not find a fingle perfon afflidted 
with the difeafe, and not above five or fix recruits had 
been dilinifled on account of defedtive vifion ; while in 
M Y O 
one of the colleges at Oxford, confiding of 125 ftudents, 
no lefs than 37 were near-lighted. 
Rule for Concave Glaffes to read and write, for a near- 
fighted Perfon. —Multiply the greateft diftance at w'hich 
the lhort-fighted fees diftindtiy with his naked eye, by the 
diftance at which it is required he Ihould fee diftindtiy by 
a concave glafs, and divide the product by the difference 
between the laid diftances. If it be to fee remote objedts, 
the focus Ihould be the fame as that required for the dif¬ 
tance of diltindt vifion. Monthly Mag. Apr. 1811.—We 
Avail have occaiion to relume this lubjedt under the article 
Optics. 
MYOP'ORUM, [a name contrived by Dr. Solander, 
to exprels the minute pellucid fpots for which the foliage 
is remarkable. The word is formed of the Gr. t uvu, to 
lhut up, and a pore; thole fpots being, as it were, 
pores clofed with fiome femitranfparent fubftance.] In bo¬ 
tany, a genus of the clals didynamia, order angiofpermia, 
natural order perfonatse, Linn, (vitices, Jiff, myoporinae. 
Brown.) Generic Charadlers—Calyx: perianthium infe¬ 
rior, of one leaf, in five deep, ovate-lanceolate, acute, 
eredt, permanent, fegments. Corolla: of one petal, fome- 
what falver-lhaped; tube Ihort, rather bell-lhaped ; leaf 
in five deep nearly-equal fegments, generally hairy within. 
Stamina : filaments four, awl-lhaped, Ihorter than the co¬ 
rolla, infertedinto its tube, two of them rather the fliorteft^ 
antheras vertical, arrow-lhaped. Piftillum : germen fu! 
perior, elliptic-oblong, comprefled, ftyle cylindrical, 
curved, the length of the ftamens ; ftigma capitate. Pe- 
ricarpium : drupe pulpy. Seed : nut ftolitary, of four or 
five cells, with lolitary kernels; or of two cells, with 
two kernels in each.— Effential Char after. Calyx in five 
deep fegments, inferior, permanent; corolla bell-fhaped; 
its limb in five deep nearly equal fegments; ftigma obtufte 5 
drupe pulpy ; nut of from two to five cells, moftiy five. 
Willdenow fuppofes this genus not diftindt from Citha- 
rexylum; but the latter has a tubular calyx, with fliort 
teeth, and two feparate nuts, of two cells each ; nor is the 
lhape of the corolla like that of the preftent genus. Thofe 
who called ftome of the fpecies Pogonia and Andreufia, 
were by no means aware of the original name publifhed, 
many years before, by Forfter. There are eighteen fpe¬ 
cies, in three divifions. 
1. Leaves alternate entire. 1. Myoporum eilipticum, or 
elliptical myoporum: leaves elliptic-lanceolate, pointed, 
tapering at the bafte ; branches fmooth ; fegments of the 
calyx lanceolate, very fharp; mouth of the corolla flightly 
hairy; limb fmooth. Native of the tropical regions of 
New Holland, as well as of the country near Port Jackfton. 
It was railed from feed in 1790, by the late Mr. Robertfon, 
at Stockwell; is readily propagated by cuttings, and flow¬ 
ers freely in January or February, though rather more im¬ 
patient of damp and cold than ftome other Ihrubs of New 
South Wales. The leaves are fmooth, like the whole of the 
genus. Flowers axillary, moftiy folitary, on footftalks, 
drooping, white, the lize of lily of the valley, but not of 
the fame hemifpherical form, their corolla being rather 
contradted in the middle, its limb fpreading fuddenly. 
There are no bradtes nor ftipules in the whole genus. 
2. Myoporum tenuifolium, or narrow-leaved myopo¬ 
rum : leaves lanceolate, with long taper points ; branches 
fmooth; fegments of the calyx lanceolate, acute; corolla 
fmooth. Native of the tropical part of New Holland. 
Gathered in the Sandwich Illands by Mr. Menzies. Dif¬ 
fers from the former in having much narrower and more 
tapering leaves ; leveral flowers, for the moft part, toge¬ 
ther ; whofe corolia is not hairy, and the fegments of 
whofe calyx are Ihorter and more ovate. 
3. Myoporum acuminatum, or pointed-leaved myopo¬ 
rum : leaves broadifh-lanceolate, with a final! point; ta¬ 
pering at the bafe; branches fmooth ; fegments of the 
calyx ovate-lanceolate; corolla bearded. Found near 
Port Jackfon, New South Wales. The dried leaves have 
a glaucous hue; and there are feveral drooping flowers 
together from the bofom of each. 
4 
4. Myoporum 
