ROD 



Proportional lengths according to Major Remiell. 

 r Thames ....... 1 



1 Rhine 51 



EUROPE J ^ 



J Danube ....... 7 



I Volga ....... 9 



'Indus ....... C| 



Euphrates ....... 8} 



Ganges ....... 9| 



Burrampooter ...... 8| t f 



.Ava River ...... 9 



ASIA... < Jiicei ....... 10 



Obi ........ 10| 



Amour ........ 11 



Lena . . ...... . 11| 



Hoang-Ho ...... . . 13J 



^ [KianKu ....... 15 



AFRICA Nile ....... 12J ' 



581 ' 38 ^ 1 ....... 8 



C Amazon ....... 15| 



S, equilibrium of.-(WhewelL) 



1. A roof A C A', consisting of beams forming an isosceles triangle 

 with its base horizontal, supports a given weight at its vertex C : the 

 weights of the beams being also given; it is required to find the hoii- 

 zouttffKrce at A and A'. 



,JLet B be the weight of the beam A C, C the weight at C, a. the angle 

 which A C makes with the horizon, H the horizontal pressure at A j 

 then 



H = 



2 tan. a. 



If there is no beam joining A A', this horizontal pressure H must be 

 counteracted by the supports on which the ends A, A' are placed. 



If te roof A C A' support a covering of uniform thickness, the formu- 

 la will still be true including in the weight B, the weight of that portioa 

 of the covering 1 which rests upon the beam. 



The weight C at the point C may arise from a longitudinal team per. 

 pendicular to the plane A A' C. 

 250 



