EXPERIMENT STATION BULLETINS. 



491 



TABLE IV. 



There will be found in columns 3 and 5, also, the readings taken for 

 determining the elevations of the remaining stakes. 



The leveling in this case is done with one. of the cheaper kinds of 

 grade level. 



In column 1 of the table are the numbers of the stakes (1 to 11). 



In column 2 is shown the distance of each stake from stake 1. In this 

 case the stakes are located 50 ft apart, so that stake 2 is 50 ft. from 

 stake 1, and stake 3 is 100 ft. from stake 1, and so on up to stake 11 

 which is 500 ft. from stake 1. 



COMPUTATIONS. 



With the fore-sight and back-sight readings recorded in the table, 

 the next step is to determine the elevations of the several stakes. If the 

 reader is sure that he understands the processes of determining the eleva- 

 tions he may disregard what follows in boldfaced type. If he is not 

 sure, it is suggested that he refer to table IV, in which there is entered 

 all the data developed to this point in the work, and that, following 

 directions below, he determine the proper values and enter them in col- 

 umns 4 and 6 of the table. 



ELEVATIONS. 



Observe that the back-siarht readin^r taken at stake 1 is introduced on the line 

 belong'in^ to stake 2, and that in like manner each back-sight reading' is introduced 

 on the line of the stake whose elevation is sought by its use. Observe, also, that 

 each fore-sight reading is introduced upon the line of the stake at which it was 

 taken. 



1. We assume the elevation of stake 1 to be 10 ft. above datum. This we 

 record on line 1 in column 6. Fig. 16 shows the location of the datum plane. 



2. Add the first back-sight reading, 4.75 ft., to the elevation of stake 1. This 

 gives 14.75 ft. as the height of the instrument above datum. The height should be 

 recorded on line 2 in column 4. Subtract the fore-sight reading, 4.25 ft., from this 

 height of instrument. This gives 10.50 ft. as the elevation of stake 2. This eleva- 

 tion we record on line 2 in column 6. 



3. Add the back-sight reading, 5.00 ft., to the elevation of stake 2. This gives 

 the height of the instrument, 15.50 ft., in its second position. Record properly. 

 Subtract from 15.50 ft. the fore-sight reading, 5.75, and we have 10.33 ft. as the 

 elevation of stake 3. This elevation we record on line 3 in column 0. 



Observe: — (1) That with each setting of the instrument one back-sight reading 

 and one fore-sight reading were taken. (2) That adding the back-sight reading to 



