120 PRELIMINARY MATTERS. 



A rental R is due now, and then after every n years, for 

 ever ; its present value is : 



r _Rxl'op n /Y , 



~ l-op'-l 



4. Conversion of an Intermittent into an Annual Rental. 



A rental R is due every n years, commencing from the 

 present time ; it is equal to an annual rental of 



-F^Ti*'*' ;. - - (XI.) 



A rental R is due after m years, and then every n years for 

 ever ; its value is equal to an annual rental of 



A rental R is due now, and again every n years for ever ; its 

 value is equal to an annual rental of 



All the above calculations can be made with logarithms, or by 

 means of tables which give future or present values for various 

 rates of interest. The Tables at page 394, which give the 

 values for Formula? I., II., VIII., and VI., suffice for all 

 ordinary forest calculations. 



SECTION IV. ESTIMATE OF RECEIPTS AND EXPENSES. 



1. Receipts. 



The receipts of forests are derived from a variety of produce, 

 which are generally divided into two classes : Major or 

 principal produce, and minor produce. 



a. Major Produce. 



This comprises all yields of wood, that is to say, timber and 

 firewood. Bark is generally included ; if it is severed from 



