OPS OPTICS. 



309 



good. A full discussion of this subject belongs to a 

 systematic work on governments ; and well would it 

 be, were there an author to treat all the parts of free 

 governments with a sagaciousness like that of the 

 immortal Florentine, in his development of absolute 

 power. Great Britain, France, and the United States, 

 are the only countries in which opposition, in the true 

 meaning of live word, as yet exists. 



OPS. See Cybele. 



OPTICS ; the science of vision, which treats of 

 the changes which light undergoes, in its qualities, 

 or in its duration, when passing through bodies of 

 different kinds and shapes, when reflected from their 

 surfaces, or when moving past them at short dis- 

 tances. For an account of the nature and more 

 general properties of light, see the article under that 

 word. 



History. The ancients seem to have been very 

 early acquainted with metallic mirrors, and we find 

 burning glasses mentioned in the Comedy of the 

 Clouds, by Aristophanes, which was enacted during 

 the fifth century before the Christian era. Pythago- 

 ras and Empedocles, who flourished in the same cen- 

 tury, both speculated on the theory of vision ; the 

 former maintaining, that objects become visible in 

 consequence of particles, from the luminous objects, 

 entering the pupil of the eye : the latter, on the 

 oilier hand, asserted, that objects become visible by 

 means of particles emitted from the eye, and striking 

 them. It is not a little remarkable that Plato, who 

 flourished about a century after, held the same opinion 

 MS Kmpedocles. The Platonic philosophers, however, 

 taught two important laws in optics, '. e., that light, 

 from whatever source it may issue, is propagated in 

 straight lines, and also, that the angle 01 incidence 

 is equal to the angle of reflection. Aristotle observed, 

 pretty accurately, the phenomena of halos, parhelia, 

 and the rainbow. Archimedes destroyed the Roman 

 fleet by fire, from the collected influence of the sun's 

 rays reflected from a great number of plane mirrors. 

 The first writer on optics on record, was the illustri- 

 ous geometer, Euclid, who flourished about the year 

 300 B. C. ; but, though from the hand of so great a 

 man, the work contains much false reasoning. Seneca, 

 about the middle of the first century of the Christian 

 era, observed the effect of a glass-bottle filled with 

 water, in magnifying objects, and also the effect of 

 prisms in colouring objects seen through them. He 

 also observed the magnifying power of concave mir- 

 rors. Claudius Ptolemy, the celebrated astronomer 

 of Alexandria, was the greatest optician of the an- 

 cients. He lived about the middle of the second cen- 

 tury, and two copies of his work still exist, one in 

 the Bodleian library at Oxford, the other in the Royal 

 library at Paris. In this work, he treats of the theory 

 of vision, or the refraction and reflection of light, of 

 mirrors and lenses; and he treated the theory of astro- 

 nomical refraction with more justice than any other 

 astronomer before the time of Cassini. Nothing 

 more was done by way of advancing optical science 

 until the beginning of the tenth century, when one 

 Al Farabius, an Arabian, produced a work on Per- 

 spective; but the only Arabian optician, whose work 

 has come down to us, is that of Alhazen, who lived 

 about the end of the eleventh century. In his work, 

 he gives a very lucid account of the theory of vision, 

 and a description of the eye ; investigates the pro- 

 perties of seven different forms of mirror, and derives 

 theorems for determining the relative distances of the 

 object, image, and eye. In 1270, one Vitello, a Pole, 

 drew up an elaborate work on optics, in which he 

 arranged the results of the labours of his predeces- 

 sors in a methodical order, and added much that was 

 new of his own. Roger Bacon, who lived during 

 the greater part of the thirteenth century, treats 



largely of optics in his Opus Maj'us, where he clearly 

 describes spectacles and the single microscope, an 1 

 has, by several historians, been considered as the in 

 ventor of these, as well as the telescope. Muschen- 

 broek states, that it is inscribed on the tomb of Sal- 

 vinus Armatus, a Florentine nobleman, who died 

 in 1317, that he was the inventor of spectacles. 

 Considerable additions were made to the science of 

 optics by Maurolycus of Messina, who published a 

 work in 1525, under the title of Theoremata de 

 famine et umbra, which contains many original and 

 profound investigations of the theory of light. To the 

 contemporary of Maurolycus, John Baptista Porta, 

 we are, in all likelihood, indebted for the invention of 

 the camera obscura, and some also claim for him 

 the invention of the telescope, which last honour is 

 also claimed for Roger Bacon, and for Thomas 

 Digges, by his son Leonard, who published a work 

 entitled Pantometria, (London, 1571), claiming 

 with great plausibility the honour of the invention 

 to his father. The invention of the telescope is 

 ascribed by Descartes to James Metius, a citizen of 

 Alkmaer, in Holland, about the year 1600. Strong 

 evidence has been given that telescopes were made 

 in 1609, by Zalmrius Jansen of Middleburg. Early 

 in the seventeenth century, M. A. de Dominis, 

 archbishop of Spalatra, by a happy experiment with 

 a glass globe, discovered the true theory of the rain- 

 bow, that it was produced by one reflection and two 

 refractions. Galileo, without any knowledge of the 

 construction of the telescope of Jansen, formed one 

 for himself at Padua, in 1609, and constructed 

 instruments of the form which generally goes by his 

 name, i. e. those composed of a convex object glass 

 and concave eyeglass, which had a magnifying 

 power of 1000 times. The illustrious Kepler, in a 

 work published in 1611, explained the theory of the 

 telescope, and proposed the employment of one or 

 more convex eyeglasses, a proposition which was 

 first duly appreciated and put in practice by Father 

 Sheiner ; and Father Reitz effected a still farther 

 improvement by employing an eye piece composed 

 of three or four convex lenses, and is in tact the 

 inventor of the common refracting telescope. The 

 doctrine of refraction was investigated by Kepler, 

 and from his experiments he obtained many impor- 

 tant results ; he also discovered many of the theorems 

 for the determination of the foci of lenses, and his 

 reasonings on the theory of vision are remarkable in 

 the history of optics for their profoundness and 

 accuracy. From the striking facts elicited by the 

 experiments of Kepler, it is remarkable that the law 

 of refraction escaped his penetrating mind ; the 

 honour of the discovery of this law was reserved for 

 professor Snellius of Leyden. The law of refraction 

 is that the sine of the angle of incidence bears to the 

 sine of the angle of refraction a constant ratio in 

 the same media. To Descartes, who flourished 

 during the first half of the seventeenth century, 

 much is due for his contributions to optical science. 

 Descartes showed that since the spherical form of 

 lenses failed to concentrate the rays in one point, we 

 must look for a perfect lens in one whose curve is 

 one of the conic sections ; and he, therefore, proposed 

 the employment of hyperbolic and elliptical lenses in 

 the construction of telescopes. Such lenses never 

 have been formed, and it is more than likely never 

 will ; nor is it at all probable that the reflecting tele- 

 scope has derived any advantage from the multi- 

 farious attempts that have been made to give the 

 specula? a parabolic form. The mechanical opera- 

 tions necessary to produce such curves seem utterly 

 impracticable ; and even if they could be produced 

 in lenses, they would only destroy the caustic curve, 

 but would not compensate for the far greater evil, 



