164 THE SEVEN FOLLIES OF SCIENCE 



9,223,372,036,854,775,808, 



and the sum of all the terms of this double progression, 

 beginning with unity, may be obtained by doubling the 

 last term and subtracting the first from the sum. The 

 number, therefore, of the grains of wheat required to sat- 

 isfy Sessa's demand will be 



18,446,744,073,709,551,615. 



Now, if a pint contains 9,216 grains of wheat, a gallon 

 will contain 73,728, and a bushel (8 gallons) will contain 

 589,784. Dividing the number of grains by this quantity, 

 we get 31,274,997,412,295 for the number of bushels nec- 

 essary to discharge the promise of the Indian prince. And 

 if we suppose that one acre of land is capable of producing 

 in one year, thirty bushels of wheat, it would require 

 1,042,499,913,743 acres, which is more than eight times 

 the entire surface of the globe; for the diameter of the 

 earth being taken at 7,930 miles, its whole surface, in- 

 cluding land and water, will amount to very little more 

 than 126,437,889,177 square acres. 



If the price of a bushel of wheat be estimated at one 

 dollar, the value of the above quantity probably exceeds 

 that of all the riches on the earth. 



THE NAIL PROBLEM 



GENTLEMAN took a fancy to a horse, and the 

 dealer, to induce him to buy, offered the animal 

 for the value of the twenty-fourth nail in his 

 shoe, reckoning one cent for the first nail, two 

 for the second, four for the third, and so on. The gentle- 

 man, thinking the price very low, accepted the offer. What 

 was the price of the horse ? 



