Students are invited to follow the thinking of a true scientist. This excerpt is from volume 3 of Travels in Brazil 1824, describing the Pororoca, the bi-annual flooding of the Amazon. Translations in many languages will hopefully be ready for the Earth Day Teach-In 2020! All plants, animals and place names will be linked to images, just as they are linked in Volumes 1 and 2.
http://remembertherainforest.com/shop2/rtr1/tvolumes/tv2p159p.html

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The Indians often consider this phenomenon as a devilry of evil spirits. The word in their language means "sea snoring or thundering."  The next Pororoca was going to occur in Guama, near the parish of Sao Domingos, the left bank of the river (50 ° 5 ' longitude west of Paris and 1 ° 27 ' south latitude).   To observe the phenomenon at that location, we were on our way on the afternoon of August 6th, in a canoe equipped with four Indians. We had only wandered 1 hour by the Guama when terrible thunder broke along the shore obscured by bushes and low trees. We were forced to pull the canoe ashore and stay there until the sunset, waiting for the incessant torrential rain to pass.  When the river began its reflux, seeing in front of us only a painful and time-consuming journey into the darkness, and finding ourselves all drenched, we decided to return to Belem and postpone our journey inland for the observation of the Pororoca.

Almost a year later, on May 2, 1820, I alone undertook this trip again. It was the full moon and I could see therefore, in all fullness, the spectacle of the prodigious phenomenon.  I departed from Belem at 9:00 at night, and took advantage of the rest of the night, with the favorable movement of the flow, rowing upriver.  The banks of the Guama are low, covered everywhere in dense forests. The river runs, in general, from southeast to the northeast direction.  In the middle of the distance between Sao Domingos and Belem, at the point where the small Inhabi river coming from the north joins it and makes a very large curve to the north. Its width is from 12 to 15 arms, and almost always quite equal; The depth varied, according to our polls: on the margins, between 8 and 12 feet; In the middle of the channel, between 12 and 20 feet. It was considered high tide and it seemed to me at the highest height of the river level, to reach more than one and a half feet.  This current, measured with keel bar, gave 35 feet in a minute; The speed of the flow rose from 25. This current is considerable in relation to other rivers; It seems, however, to increase even further as the Guama flows, although this river, while running west, has only low margins, and just beyond the village of Ourem, running from south to north, makes its way through low hills covered in woods.

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We sailed only during the hours of the high tide, as is usual in all the coastal rivers of this region, because the opposite would be too tiring for our paddlers, and in any case the trip needed to be made with certain pauses.  Mocajuba, an opulent farm on the riverbank, gave us an inn, during the first part of the night from  May 26 to 27. The banks of the Guama are fertile, and crops thrive there, especially good sugarcane. There was also a large rum distiller. The Carmelites of Para, along this river, possess several farms, run by the convent, while they export meat and other products from their pastures on the island of Marajo. With the return of the high tide, about 1:00 in the morning, we continued the journey, and, at 9:00 in the morning, we reached Sao Domingos, a poor parish on the eastern shore of the Guama River, above the confluence of the Guama with the Capim River, whose distance from Belem is evaluated by 16 leagues. The barometer, upon our arrival, was 27  ", 9 " ', while the thermometer, 9 hours beforehand, in the open air, indicated 25 ° R., and in the water of the river, 21.5 ° R. The mercury column stayed all day in equal height, and rose 0.4 lines between 1:00 and 2:00 in the afternoon. At 6:00 in the afternoon the thermometers indicated, in the air, 22 °; and water 20.5 °.

The Pororoca should, according to the regular periodicity of the flow and reflux, occur after midnight. Because the moon, on that day, passed the meridian one minute before midnight,  I did not lose a minute posting myself in a small elevation along the river where you could watch the show. At 1 hour and a half, I heard a mighty roaring, similar to that of a large waterfall. I looked downstream, and at the exact quarter of an hour, there appeared a great wave of some 15 feet tall, a wall that spanned the width of the river, precipitating forward rapidly, with a dreadful commotion, while the waters of the river foamed mightily, always in opposition to the flood. At some points, near the shore, the water was lowered in the width of one or two arms, but it was soon elevated again by the river above, where the waves, assembling without ceasing, were driving the swim forward.  As I was astonished at looking at this periodic revolt of the waters, suddenly the mountain of water beneath the confluence of Capim with the Guama sank twice, while they were swelling and spreading wide shallow waves, forming small swirls,in the surface of the river. However, as soon as the roar of the first advance was extinguishing, the waters were restored, they were forming into a living wall with a strong snoring and shaking in the 

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foundations of the river banks, as they precipitate from the sparkling ridge of new water rearing almost  as high as it had been, separating itself in two arms by the rivers above, where they soon vanished from my sight. The whole phenomenon had only lasted less than half an hour. The receding waters, which, however, as well as the waves of the Pororoca, were not at all blurred by the mud, and were then at the point of greatest flood,  little by little quietening, and they are consumed, after short term, emptying visibly, to where the reflux began. The residents of Sao Domingos told me that during the lunar phases, the reflux lasted longer, up to 9 hours; The other days, however, were from 1 to 2 hours shorter. The period of the river’s low tide lasts from 6 to 7 hours, and being replaced by a long high tide, extends, therefore, here, toward the invading wave.  It requires 1 hour or 80 minutes to propel all the water mass up the river. The water, which we harvested soon after the Pororoca had no salty flavor, was not much more cloudy than usual. The Pororoca is carried, however, only to a river below Sao Domingos and 12 leagues into the surrounding areas, and in the streams, while the lower regions of the Guama always has flow and reflux regularly, invading with all its phenomena the neighboring shores of Ocean. 

Also not all the places of the upper course of that river are disturbed by the Pororoca. At various points, which must always be of considerable depth, the Pororoca is low, below the confluence of the Capim with the Guama, and rises anew, in the supposed shallower parts of the riverbed,  and in the end, with equal impetus, precipitates up the river above. These quiet places are called “gifts from God “ by the inhabitants. In them, too, in any case, the water rises, when the ocean rises. But it reaches the highest height, without any impetuous movement by 1:30 to 2 hours, after the highest water.  These “gifts from God” are unequal distances and so distant from each other that they do not coincide with the points that suffer, at the same time, the greatest emptying. It follows, therefore, that the Pororoca does not influence the regulation of the river that makes its way, it goes when it wants to, and then one must wait it out in a “gift from God". The most impetuous Pororoca of the Guama are carried out along with the high seas of the coastline, in the phase of the full moon and the new moon, but particularly in the months of March, April and September, in the equinoxes, therefore. I still see, in the Church of Sao Domingos, the vestiges of the devastation caused by the shocks of the Pororoca of  this past April. This church is in danger of being destroyed totally by the Pororoca, which loosened the land in the neighborhood, just as..... to be continued