USEFUL TO THE MICROSCOPIST 1135 



Geometrical Progression 

 m, multiplier or divisor. 



B B in A 



A= . -B = A in ( " ' i >. b = 



m ( " m 1 



Properties of Circles and Spheres <<T. 



77 = 3-141592653589793 + log TT = 0-4971498727 



77- = 9-8696 A/?7= 1-77245 =-31831 



77 



1 = -10132 - = -56419 - = -785398 



77~ A/77 



- = -5236 A/2 =1-41421 



Circumference, C. Area, A. Radius, r. Diameter, d. Volume, V. 



Surface, S. 



x?3 / ' 



/-If) T * O 1'' \T y7 



6 ' ~TT' 



,. - degrees in arc x. area of circle 

 Area of sector of circle = . 



Length of arc = number of degrees x -017453 r. 



Unit of circular measure = 57'2957S. 



Side of square of equal area to a circle = r \/TT. 



Side of inscribed square / \/2. 



Area of ellipse = ^ major axis x i minor axis x 77. 



Volume of spheroid = polar axis x (equatorial axis)- -. 



6 



Number of Threads per inch in Whitworth's Standard Screws 

 Sizes ^ . . No. of threads 150 Sizes . No. of threads 20 



A 80 



^ CiO 



i: B'l ' " 



* . 40 



., ^j . . ,, 32 



,,. 



I . . 16 



A 14 



A - . 12 



,, 



Convenient Approximations for rapid Calculations 



6 knots = 7 miles, more correctly 13 knots = 15 miles. 



8 kilometres =5 ,, ,, 50 kilometres = 31 ,, 



1 metre = 3 ft. 3^ in. 32 metres = 35 yards. 



5 centimetres = 2 inches ,, 33 centimetres 13 inches. 



3 millimetres = inch .. 5 millimetres = J inch. 



1 pole = 5 metres ; 1 furlong = 2 hectometres. 



5ft = -nW inch ; T fa inch = mm. ; T uoWo incl1 = ? M- 



2 are = 239 sq. yds ; 1 rood = 10 are ; 2 acres = 81 are ; 100 hectare 

 = 247 acres ; 3 cubic yards = 23 decisteres ; 1 decastere = 13 cubic yards ; 

 2 decilitres = 7 / 5 (ounces) ; 4 litres = 7 pints ; 2 grammes = 31 grains ; 



