182 Scientific Intelligence. — Meteorology. 



what contracted. The tide flows up past Para with great velocity, 

 and entering the Guama river comes to the narrow part of the chan- 

 nel. Here the body of tidal water will be deeper and flow faster, and 

 coming suddenly on to the shoal will form a wave, in the same manner 

 that in a swift brook a large stone at the bottom will cause an un- 

 dulation, while a slow flowing stream will keep its smooth surface. 

 This wave will be of great size, and, as there is a large body of wa- 

 ter in motion will be propagated onwards unbroken. Wherever there 

 are shallows, either in the bed or on the margin of the river, it will 

 break, or as it passes over slight shoals will be increased, and as the 

 river narrows will go on with greater rapidity. When the tides are 

 low they rise less rapidly, and at the commencement a much less body 

 of water is put in motion ; the depth of the moving water is less, 

 and does not come in contact with the bottom in passing over the 

 shoal, and so no wave is formed. It is only when the body of water 

 in motion as the tide first flows in is of sufficient depth, that it comes 

 in contact with the shoal, and is, as it were, lifted up by it, forming 

 a great rolling wave. It appears, therefore, that there must exist 

 some peculiar formation of the bottom, and not merely a narrow- 

 ing and widening in a tidal river to produce a bore, otherwise it 

 would occur more frequently than it does. — (Travels on the Amazon 

 and Rio Negro, by Alfred R. Wallace, p. 114.) 



7. Mirage of South Africa. — We were surrounded by a mirage 

 of the most remarkable intensity, — objects 200 yards off were ut- 

 terly without definition ; a crow, or a bit of black wood, would look 

 as lofty as the trunk of a tree, — pelicans were exaggerated to the 

 size of ships with the studding sails set, and the whole ground was 

 wavy and seething, as though seen through the draught of a furnace. 

 This was in August, the month in which mirage is most remarkable 

 here ; it is excessive at all times, and has been remarked by every 

 one who has seen the place. A year and a half later [ tried on 

 two occasions to map the outline of the bay, which was then com- 

 paratively clear, but still the mirage quite prevented me ; an object 

 which I took as a mark from one point being altogether undistin- 

 guishable when I had moved to my next station. — (The Narrative 

 of an Explorer in Tropical South Africa, by Francis Galton, 

 p. 16.) 



8. Majestic Cloud seen from the Jungfrau. — It was four o'clock 

 when we reached the summit of the Jungfrau, and we staid half an 

 hour. The view to the east was generally clear. The Finsteraar 

 and Schreckhorn, the glacier of Aletsch, the Monch and Eigher, — 

 and we got a glimpse of the bottom of the valley of Grindelwald. 

 The view to the west was in one respect scarcely less remarkable, 

 for there a magnificient cumulous-headed cloud stood in wonder- 

 ful majesty, reaching apparently from the valley to at least 2000 

 feet above us. It was a glorious sight, a single cloud at least 10,000 

 feet high. — (Norway and its Glaciers, by Frof. James Forbes.) 



