544 
OPT 
and Arabic, we fee how much the love of fcience was now 
excited, and what effects the art of printing was now be¬ 
ginning to produce. 
Baptifta Porta’s difcovery fuggefted a hint to Kircher, 
of winch he availed himfelf by the conftrufiiion of the 
magic lantern, doing that in the night, and in many re- 
ipedls more conveniently, which Porta exhibited in the 
day. 
The conftitution of the eye, and the funftions of the 
different parts of which it confifts, were not yet fully un- 
derftood. Maurolycus had nearly difcovered the fecret; 
and it was but a thin, though to him an impenetrable, 
veil, which ffill concealed one important part of the 
truth. This veil was drawn afide by the Neapolitan phi- 
lofopher ; but the complete difcovery of the truth was 
left to Kepler, who, to the glory of finding out the true 
laws of the planetary fyftem, added that of firfl: analyzing 
the whole f'cheme of nature in the ftru&ure of the eye. 
He perceived the exa< 5 t refemblance of this organ to the 
dark chamber, the rays entering the pupil being collected 
by the cryftnlline lens, and the other humours of the eye, 
into foci, which paint on the retina the inverted images 
of external objects. By another ftep of the procefs, to 
which our analyfis can never be expected to extend, the 
mind perceives the images thus formed, and refers them 
at the fame time to things without. It feemed a great 
difficulty, that, though the images be inverted, the objefifs 
are feen ereft; but, when it is confidered that each point 
in the object is feen in the direftion of the line in which 
the light paffes from it to the retina, through the centre 
of the eye, it will appear that the upright pofition of the 
objefif is a neceflary confequence of this arrangement. 
Kepler’s difcovery is explained in his Paralipomena in 
Vitellionem (Remarks on the Optics of Vitello), a work 
cf great genius, abounding with new and enlarged views, 
though mixed occafionally with fome unfound and vi- 
fionary fpeculations. This book appeared in 1604. But 
we fhall prefently have occafion to return to the confide- 
ration of other parts of Kepler’s optical difcoveries. 
The rainbow had, from the earlieft times, been an ob¬ 
ject of intereft with thofe who beftowed attention on op¬ 
tical appearances -, but it is much too complicated a phe¬ 
nomenon to be eafily explained. In general, however, it 
.was underftood to arife from light refletted by the drops 
of rain falling from a cloud oppofite to the fun. The 
difficulty feemed to be how to account for the colour, 
which is never produced in white light, fuch as that of 
the fun, by mere reflection. Maurolycus advanced a con- 
flderable ltep when he fuppofed that the light enters the 
drop, and acquires colour by refradion ; but, in tracing 
the courfe of the ray, he was quite bewildered. Others 
fuppofed the refraftion and the colour to be the effeCt of 
one drop, and the refleftion of another; fo that two re¬ 
fractions and one reflection were employed ; but in fuch a 
manner as to be ftill very remote from the truth. An¬ 
tonio de Dominis, archbiffiop of Spalatro, had the good 
fortune to fall upon the true explanation. Having placed 
a bottle cf water oppofite to the fun, and a little above 
his eye, he law a beam of light iifue from the under fide 
of the bottle, which acquired different colours, in the 
fame order, and with the fame brilliancy, as in the rain¬ 
bow, when the bottle was a little railed or deprelfed. 
From comparing all the circumftances, he perceived, that 
the rays had entered the bottle ; and that, after two re- 
fraftions from the convex part, and a reflection from the 
concave, they were returned to the eye tinged with diffe¬ 
rent colours, according to the angle at which the ray had 
entered. The rays that gave the fame colour made the 
fame angle with the furface, and hence all the drops that 
gave the lame colour mult be arranged in a circle, the 
centre of which was the point in the cloud oppofite to 
tire fun. This, though not a complete theory of the 
rainbow, and though it left a great deal to occupy the at¬ 
tention, firfl: of Des Cartes, and afterwards of Newton, 
was perfectly juft, and carried the explanation as far as 
ICS. 
the principles then underftood allowed it to go. The 
difcovery itfelf may be confidered as an anomaly in fci¬ 
ence, as it is one of a very refined and fubtle nature, 
made by a man who has given no other indication of 
much fcientific fagacity or acutenefs. The book con¬ 
taining this difcovery was publifhed in 1611 at Venice, 
in 4to. 
A difcovery of the fame period, but fomewhat earlier, 
will always be confidered as among the molt remarkable 
in the whole circle of human knowledge. It is the in¬ 
vention of the te/eJ'cnjie, the work in which (by following 
unconfcioufly the plan of nature in the formation of the 
eye) man has come the neareft to the conftruCtion of a 
new organ of fenfe. For this great invention, in its ori¬ 
ginal form, we are indebted to accident, or to the trials 
of men who had little knowledge of the principles of the 
fcience on which they were conferring fo great a favour. 
A feries of fcientific improvements, continued for more 
than two hundred years, has continually added to the 
perfection of this noble inftrument; and has almoft en¬ 
titled fcience to confider the telefcope as its own pro¬ 
duction. 
It is the common opinion, that we owe the firfl: inven¬ 
tion of the telefcope to James Metius ; and it is placed 
at the beginning of the feventeenth century. Such, too, 
is the fentiment of Des Cartes, who wrote in Holland about 
thirty years after the difcovery. On this fubjeCt, he ex- 
prefles himfelf as follows, at the beginning of his Diop¬ 
trics : and, though the paflageis fomewhat long, perhaps 
the reader will fee it here with pleafure. “ The whole 
conduCl of our life depends on our fenfes, among which 
that of fight, being the molt noble, and the moft univerfal 
in its application, it is unqueftionable, that thofe inven¬ 
tions which increafe its power are of all the moft ufeful. 
And it is not ealy to find one that (hall increafe it more 
than thofe wonderful telefcopes, which, though their date 
is fo recent, have already difcovered new ftars in the fir¬ 
mament, and other new objefts upon earth, in greater 
number than thofe we had feen before ; fo that, extend¬ 
ing our view much farther than the imagination of our 
forefathers had been able to reach, they feem to have 
opened to us a path, by which we may attain a much 
greatir and more perfeCt knowledge of nature than they 
pofiefled. It is about thirty years fince James Metius, of 
the town of Alcmaer in Holland, a man who had never 
ftudied, though he had a father and a brother profeffors 
of mathematics, but who took particular delight in making 
mirrors and burning-glafles, forming them in winter even 
of ice, as experience has fnovvn may be done, having, on 
this account, glalfes of various forms, fortunately thought 
of looking through two, one of which’ was a little thicker 
at the centre than at the edges, the other, on the contrary, 
much thicker at the edges than in the centre ; and he ap¬ 
plied them fo happily to the two extremities of a tube, 
that the firfl: of the telefcopes of w hich we Ipeak was com- 
pofed ; and it is wholly after the pattern of this, that all 
the others we have fince feen were made, &c.” 
Others relate, that the children of a fpe£tacle-maker 
of Middleburg in Zealand, with whofe name we are un¬ 
acquainted, playing in their father’s Ihop, remarked, that 
when they put two fpe&acle-glalfes one before the other, 
and looked through them both at the weathercock »f a 
neighbouring fteeple, it appeared larger than ufual. The 
father, ftruck with this Angularity, thought of adjufting 
two glalfes on a board, by means of brafs rings, which 
might be brought nearer to each other, or farther off, at 
pleafure. Thus he was enabled to fee better, and at a 
greater diftance; and at length proceeded to place the 
glalfes in a tube, and thus formed a telefcope. Bojjut's 
Hijh. Gen. des Mathematiques. 
The late lamented Mr. Profelfor Playfair alfo gives the 
honour of the invention to the town of Middleburgh, and 
mentions the names of the parties : “ Two different 
workmen belonging to that town, Zachariah Jans and 
John Lapprey, have teftimonies in their favour between 
which 
