CONTENTS OP CISTERNS. 237 



domestic animals of the farm when other supplies fail, if 

 cisterns large enough to hold it were only provided. 

 Generally speaking, none at all are connected with barns 

 and out-buildings, and even when they are furnished, 

 they are usually so small as to allow four-fifths of the 

 Avater to waste. 



If all the rain that descends in the Northern States of 

 the Union should remain upon the surface, without sink- 

 ing in or running off, it would form, each year, a deptli 

 of about three feet. Every inch that falls upon a roof 

 yields two barrels for each space ten feet square; and 

 seventy-two barrels a year are yielded by three feet of 

 rain. A barn thirty by forty feet supplies annually 

 from its roof eight hundred and sixty-four barrels, or 

 enough for more than two barrels a day for every day in 

 the year. Many farmers have in all five times this 

 amount of roof, or enough for twelve barrels a day, year- 

 ly. If, however, this water were collected, and kept for 

 the dry season only, twenty or thirty barrels daily might 

 be used. 



In order to prevent a waste of water on the one hand, 

 and to avoid the unnecessary expense of too large cisterns, 

 their contents should be determined beforehand by calcu- 

 lation. 



RULE FOR DETERMINING THE CONTENTS. 



A simple rule to determine the contents of a cistern, 

 circular in form, and of equal size at top and bottom, is 

 the following : Find the depth and diameter in inches; 

 square the diameter, and multiply the square by the deci- 

 mal .0034, which will give the quantity in gallons* for one 

 inch in depth. Multiply this by the depth, and divide by 



* Tlu3 is the standard gallon of 231 cubic inches. The gallon of the 

 State of New York contains 221.181 cubic inches, or 6 pounds at its 

 maximum density. 



