36 Subtropical Vegetable-Gardening 



that one of these machines will raise depends on the height 

 it is being raised and the amount that is flowing in the 

 stream which supplies the water. Under the most favor- 

 able conditions, a ram will raise f of the flowing water 

 4 feet, if there is a fall of 2 feet ; or it may raise ^V ^^ the 

 water 120 feet above the source if there is a fall of 12 feet. 

 The amount raised varies inversely as the height to which 

 it is to be elevated. These rams are made in various sizes 

 to suit the conditions ; they are made to discharge from 

 I to 30 and even more gallons a minute. The cost of these 

 machines varies from $9 to over $100. Like all other 

 machines they will in time wear out, but their structure is 

 so simple as rarely to get out of order. The manner of 

 placing the tank or reservoir must be modified to suit the 

 individual fields. 



Windmills are more largely employed for lifting water 

 to tanks ; but they are more difiicult to keep in repair and 

 also wear out in a few years. Gasoline engines are now 

 commonly used and are most satisfactory; though they 

 are the most expensive of the various machines used for 

 the purpose of lifting water. 



Some method of irrigation is of great use in tropical 

 countries. Indeed without irrigation, vegetables can 

 hardly be raised during the dry season, which often in- 

 cludes most of the cool season. In tradewind regions, an 

 aermotor usually gives satisfaction as a means of raising 

 water. 



IRRIGATION 



Climatic conditions in most tropical and subtropical 

 countries are such that during a part of the year there is 



