An Experimental Study of Field Methods. 
553 
design, as it is at present so generally done; but, instead, using 
rods divided into standard units of length, and then computing 
true distances by means of an interval factor. By means of a 
table, such computations can be made very quickly. All the 
measurements discussed by this paper were thus computed. 
This point is very ably discussed by Mr. J. L. Van Ornum, of 
Washington University, in a paper on stadia work to be read 
before the coming convention of the American Society of Civil 
Engineers. He names the following as some of the disadvant¬ 
ages of the present method, as compared with that method em¬ 
ploying an interval factor. 
1st. Subsequent tests of interval cannot be made without the 
expense of repainting and regraduating the rod. 
2d. Bods cannot be interchanged among transits. 
3d. Old rods cannot be used with new transits. 
4th. Rods cannot be used in leveling without computing the 
necessary correction. 
5th. Beveling rods cannot be used as stadia rods. 
6fch. Observers with different personal equations cannot use 
the same rods without causing accumulative errors. 
These disadvantages of the present system are so evident, 
that the adoption of the interval factor method seems only a 
question of the time necessary “ to teach old dogs new tricks. ” 
The second objection to exercising greater care on the interval 
determination is more apparent than real. Increased accurracy 
of any work generally involves increased care or money, or per¬ 
haps both. The real question is, will the results of such care 
justify the increased cost? ft has been shown, that such care 
prevents, in great measure, the large systematic errors, which 
up to the present, have confined the use of the stadia method 
within narrow limits. As a matter of fact, on some of the sur¬ 
veys with which the writer is acquainted, the cost of the steel 
tapes worn out in making measurements, where the stadia 
method should have been employed, has exceeded the cost of 
either repainting the rods or the cost of the increased care in 
the interval determination. 
Again it should be noted, that in surveys furnishing frequent 
