IO 
A curious phenomenon is the cold spell of three days (dtas de 
friagern ) which may occur in the month of June. It is usually 
preceded by some heavy rains, mists and squalls. A very cold 
southerly wind occurs, accompanied by a rapid fall of temperature, 
reaching i6° C. in a few hours. In 1907 the friagern occurred in the 
first week in July, the temperature falling to 1 8° C. 
The topography of Manaos is well seen on the accompanying 
plan. From the river bank the ground gradually rises towards the 
North, where a watershed causes the formation of two igarapes 
(creeks'), the Igarape da Cachoeira Grande on the West and the 
Igarape da Cachoeirinha on the East. The city is intersected from 
North to South by the Igarapes Manaos and Bittencourt, while a 
small one, the Igarape da Castelhana on the eastern side empties 
into the Igarape da Cachoeira Grande. The Igarapes Cachoeira 
Grande and Cachoeirinha form very large collections of water at ill 
times of the year. 
The rise and fall of the Rio Negro is an important factor, there 
being a difference of 50 to 60 feet between highest and lowest river 
(Chart). I he river is at its height in June, and then gradually recedes 
until the end of October. A slight rise may occur in November and 
be followed by a further slight fall. It then remains stationary until 
January, when it commences to rise. At low river, in consequence, 
the upper reaches of the smaller Igarapes Manaos. Bittencourt, etc, 
are dried up and, as the water recedes, many puddles and holes 
containing water are left to furnish breeding-places for mosquitos. 
At high river, the water from the Rio Negro has backed up in the 
igarapes, and vast areas of low-lying land are completely submerged 
The offices of many of the chief commercial firms and banks being 
situated along the river front, an extremely high river causes much 
inconvenience and damage, as the cellars and low-lying sections of 
the streets become flooded. Since this condition persists for several 
collttin TT gat, ° n ° f and disease is favoured by these 
collections of stagnant water. The effective functioning of the low- 
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