Oporto contains four suburbs, seven parishes, ten churches, twelve convents, and nine hospitals ; a thea tre, and a kind of circus, which is a handsome building. It is partly surrounded by an old wall, five or six feet thick, flanked at intervals with mean-looking towers. The quay, which is of a simple construction, extends the whole length of the town. On one side of it is a street, and the other side of it is walled and raised, though merely for the purpose of making ships' cables fast.
The harbour of Oporto, formed by the river, is diffi 'ult of entrance, from rocks rising out of the sand, The harbour of Oporto has been gradually filling up by the sand washed down by the river. Endeavours, however, have been made to keep the stream in one place, so as to wash the sand away. The entrance to the harbour is defended by a small fort, San Jaoa de Fez, near which is a small market town. Besides this, there is on the coast, to the north, a harbour ; on the beach opposite to which, on the south side, is also a very small fort, called Santa Caterina, with a few other batteries.
There is a very agreeable walk up the river, which forms a principal object to the right ; and to the left is a steep rocky declivity, on an eminence opposite to which is a monastery with its woody quinta. The country at a greater distance is very beautiful, and forms cheerful hills. Another walk of the same kind accompanies the river down to the sea.
In winter, the climate of Oporto is damp and foggy ; and though the air is cool, yet it seldom freezes. In the summer the heat is very great. The gardens round Oporto are beautiful and pleasant, and the plants of the Cape and of NCNV Holland grow in the open air. Population about 70,000, East Long. 8° 36' 9". North Lat. 41° 8' 56°. See Link's Travels in Portugal, p. 320; and Dcscripcao Topograjica Ifistorica cla ci dade do Porto, por Agostinho Rebell° da Costa. Porto, 1789.
OrTtes, derived from the Greek word onr.rop.xt, I see, is that branch of natural philosophy which treats of the nature and properties of light, and of the changes which it experiences, either in its quali ties or in its direction, when transmitted through bodies either natural or artificial ;—when reflected from their surfaces ;—or when passing by them at a small distance.
Although history has not handed down to us the early speculations of philosophers respecting some of the more striking phenomena of optics, yet there can be no doubt that they must have been observed and studied in the earliest periods of civilization. If the nature °flight and colours, and the general phenomena of vision, were subjects too profound for their investigation, they could not fail to acquire some knowledge of the reflexion of light, and the formation of reflected images. Even the rudest savage must have observed with wonder the in verted picture of himself or of his companion, formed hy the surface of the water ; and in the reflected land scape, or in the image of a few bushes on the margin of a lake, the humblest inquirer might have found an as semblage of experiments, from which the general law of reflexion might be easily inferred.
Aletallic mirrors, however, seem to have been in ge neral use, and glass itself manufactured, long before any of the speculations of the ancients were recorded. 'Mir rors of metal are distinctly mentioned in the books of Job and Exodus ; and Pliny informs us, that glass was accidentally discovered by the dealers in nitre who tra versed Phcenicia. Being desirous of cooking their food on the banks of the river Belus, and having no stones to support their tripods, they substituted pieces of nitre ; and found, to their great surprise, tbat the matter of the tripods incorporated itself with the nitre, and formed small streams of a transparent mattcr, which cooled into glass.
The invention of (Aiming lenses of glass seems to have speedily followed the discovery of the art of glass making. In the second act of Aristophanes' comedy of the Clouds, which was performed in the year 424., B. C. burning lenses are mentioned in the most unequivocal manner; and Strepsiades remarks to Socrates, that he has no doubt seen, in the hands of the druggists, the fine transparent stone with which they light the fire. So crates asks him, if it is glass that he speaks of, and Strepsiades, replying in the affirmative, adds, that by holding this stone to the fire, he could, at a distance, melt any writing of assignation,* and thus free himself from his debts.