954 
Journal of Agricultural Research 
Vol. V. No. 20 
purposed to take readings are marked on this line. At these points a 
steel block, G f 2 inches in diameter, is placed, in order to avoid measuring 
tfie small local inequalities in the road surface. In the top of this block 
a flat-bottomed cylindrical recess is made, and an ordinary inside microm¬ 
eter is held in the recess, while its upper end is adjusted to contact with 
the steel wire stretched across the road. An electric buzzer, H, is mounted 
on the side of this block, and when contact is made between the micrometer 
and the wire an electric circuit is completed through the buzzer. With 
this instrument readings for wear may be taken to the nearest 0.001 
inch, although this degree of accuracy will not be necessary. 
Holes in the road in which the bronze plugs are set are drilled by 
means of a special hand-operated drill press carrying a star drill. 
In Plate LXVI, figure 2, the method of mounting the apparatus in 
the road and its manipulation are plainly shown. On the left is the 
heavier end block carrying the batteries, and on the right is the lighter 
block the weight of which supplies constant tension to the fine steel 
wire, part of which is seen in front of the operator. The cord extending 
on the road surface from the heavier block to the small steel block carry¬ 
ing the micrometer is one of the leads from the battery to the electric 
buzzer. 
Placing the buzzer in this position near the operator obviously is 
advantageous, especially when the instrument is to be used amidst the 
distracting noises of traffic. The end blocks are set as near to the sides 
of the road as practicable, in order to permit measurements being taken 
across almost the entire width of the road. Should longitudinal cracks 
develop through the sections measured, the readings so taken will be 
rendered useless; and in order to eliminate this difficulty, sufficient plugs 
must be set to permit obtaining readings at uncracked sections. 
Wear measurements of this kind taken of the actual road surface 
should prove of great future value if the traffic conditions and the phys¬ 
ical characteristics of the concrete materials likewise are known, and 
should help to decide present moot questions regarding concrete roads 
and road materials. Not only may concrete surfaces be measured for 
wear in this manner, but the wear or vertical movement of other kinds 
of road surfaces may likewise be determined by the use of this instrument. 
