^14 FOEESTEY WOEK 



Subsequent measurements, however, prove that the 

 metre has been made too small, so it is now defined as the 

 length of a certain bar of iridio-platinum preserved in 

 the Bureau des Archives, Paris. 



The unit of length is the Metre. 



Tiie unit of area is the Are = 100 square metres. 



The unit of solid measure is the Stere = 1 cubic metre. 



The unit of weight is the Gramme. 



The unit for dry and fluid measure is the litre. 



The litre = 1 cubic decimetre (^th of a metre) and weighs 

 I kilogramme = 1000 grammes. 



CALCULATION OF AREAS, ETC. 



Area of square = any side multiplied by itself. 



„ rectangle = length x breadth. 



„ parallelogram = base x perpendicular height. 



„ rhombus or rhomboid ... = base x height. 

 „ trapezoid (2 sides parallel) = mean length of sides x per- 

 pendicular distance be- 

 tween them. 

 „ trapezium = half the sum of the perpen- 

 diculars X by the diagonal 

 on which they fall. 



„ triangle = | base x perpendicular height. 



„ equilateral triangle .... = square of side x 0433. 



„ circle = „ diameter x -7854. 



,, „ = ,, radius x 3*1416. 



,, „ = circumference x diameter -^4. 



,, „ = radius x diameter x 1'57. 



,, ellipse — long axis x short axis x 



0-7854. 



Circumference of circle = diameter x 3'1416 or ^f*. 



Diameter of circle = circumference x 0-3183. 



,, „ equal in area to square = side x 1-1284. 



„ „ circumscribing square = side x 1-414. 



Side of square in circle = diam. x 0-7071- 



„ „ equal to circle = „ x 0-8862. 



Solid content of cylinder = area of one end 



x length. 



