44 ^^^^ Viagraph. 



the special reason that in point of amount and weight of traffic 

 it may compare with the one below it, our own awful example 

 of a main road. This last diagram was taken in December near 

 Lambeg, a part of the road which b.ad been thoroughly coated 

 with stone and steam-rolled in the previous August, The 

 Prescot road had also been repaired just about four or five 

 montlis before this test was taken last May, so that the com- 

 parison as regards lapse of time since each was repaired is fair. 



The diagram of the Prescot road is an average specimen, and 

 was not taken from the best part of this road. Further 

 comment on the comparison between these roads is almost 

 superfluous, but it may be noted that, while the greatest depth 

 of ruts generally found on these Enghsh roads is usually a 

 fraction of an inch, those on the Lisburn and other Irish main 

 roads quite commonly exceed i inch in depth, and can easily 

 be found over 2 inches, as in the diagram above. 



The index of unevenness, as measured in the manner described 

 above foreachofthethreeroads,ofwhichdiagramsare here given, 

 is as follows : — For the Gilford road the sum of the depths of 

 ruts is 12 to 14 feet per mile ; for the Prescott road, 42 feet 

 per mile (an average of all the indications taken) ; for the 

 Lisburn road in the part here taken, 134 feet per mile. 



Besides the discomfort of travelHng and the extra wear and 

 tear on vehicles entailed by such roads as this last, there is 

 another objection distinctly brought out by the viagraph. In 

 considering the passage over a rough road of a carriage wheel 

 we may probably assume that there is no impetus gained in 

 dropping into a rut which is available as a help to rise out t fit 

 at the other side. We may therefore conclude that the po\, er 

 necessary to raise the wheel out of each and every rut must be 

 supplied from the horse or other tractive force. We may 

 accordingly take the sum of unevenness as representing in 

 effect an artificial hill interposed by the badness of the road. 

 On our Lisburn road, for instance, taking the average sum of 

 unevenness as 100 feet per mile, we have an artificial hill of 

 that amount in each mile ; consequently any vehicle making 



