Sir Robert Stawell Ball's

Schoolchild's Earth/Moon

Plum-pudding problem

 

 

Fig. 31 - Relative Sizes of the Earth and the Moon

  

 

"It will require only a little care on the part of the cook to make a pair of luscious plum puddings that shall fairly set forth the sizes of the earth and moon. There is first to be a nice little round plum-pudding, 3 inches in diameter. It is just a little bigger than a cricket ball...One boy of sound constitution could eat it all. Perhaps it would weigh about three-quarters of a pound. This little globe is to represent the moon.

   Another plum-pudding is to be constructed, which will represent the earth (Fig.31). We must, however, beg the cook to observe the proportions...Hence, as the small plum pudding was 3 inches across, the large one must have a diameter of 12 inches. This will be a family pudding of truly satisfactory dimensions; perhaps the cook will be a little surprised to find the alarming quantity of materials that will be required to complete a sphere of plum-pudding a foot in diameter.

   These models having been duly made, and boiled, and placed on the table, we are now to propose the following problem:

   If one school-boy could eat the small plum-pudding,

how many boys would be required

to dispose of the large one?

   The hasty person, who does not reflect, will at once dash out the answer: Four!

 

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— from —

Star-Land, being talks with young people about the wonders of the heavens

by

Sir Robert Stawell Ball, Royal Astronomer of Ireland; Cassell & Co,1890

 

("It has long been the custom at the Royal Institution of Great Britain to provide each Christmastide a course of Lectures specially addressed to a juvenile audience")