50 



HYDROGRAPHY. 



the light cannot be seen from haze or thick weather, the soundings, 

 as well as a fall in the temperature of the water, will indicate a proxi- 

 mity to the land. The soundings extend some 25 miles, and are of 

 ooze and shells. The lighthouse on Cape Frio we found to be 1285 

 feet above the level of the sea, placed on the highest peak of the 

 island, and often enveloped in mists and clouds. Its position ap- 

 pears to have been chosen that it might be seen from as many points 

 as possible. It is a revolving light, and can be seen distinctly from 

 30 to 35 miles in clear weather. As this is a point which is always 

 made by our ships, and from whence their departure is usually mea- 

 sured, it was deemed important that its correct position should be 

 ascertained : this was effected by connecting it with the observatory 

 on Enxados Island, the position of which had been determined by a 

 series of moon-culminating stars. Sound was employed as the most 

 convenient and expeditious mode to measure the meridian differ- 

 ence : the result placed the lighthouse on Cape Frio in longitude 

 42° 00' 13" 87'" west. 



It has been generally supposed that it was necessary for vessels to 

 await a favorable wind to enter and depart from Rio Janeiro, but 

 this is a mistake ; there is no difficulty whatever in vessels departing 

 or entering, at any hour and with any wind and favorable tide : the 

 best time, however, to enter is during the day, when the sea-breeze is 

 fresh : it ordinarily dies away at sunset, and then remains calm until 

 an early hour in the morning, when a gentle land-breeze prevails 

 until about 9 o'clock. 



So safe and free from danger is this harbor, that pilots are un- 

 necessary, but it is requisite to pay attention to the tides, which at 

 times run with great velocity. There are times, too, when heavy 

 squalls prevail, from the southwest to northwest, which sometimes 

 blow with violence, and I have been informed that a heavy sea has 

 been experienced at the anchorage in the harbor, so much so as to 

 prevent any landing at the Great Quay, and rendering it necessary 

 for boats to seek the upper or mercantile harbor to land, where it is 

 practicable at all times. Vessels lie at anchor, and lighters are em- 

 ployed to land all goods, thereby causing a detention, as well as ex- 

 pense, in discharging the cargoes. 



The situation of the upper harbor is well adapted for the erection 

 of wharves, and they might be constructed with little expense, and 



