CONSTANT SUPERVISION. 277 



compressing and raising water in its flow, its destructive power 

 is largely increased. Comparatively weak structures will often 

 outlive stronger ones simply by this wise foresight. 



It seems more important that these works should be thor- 

 oughly built upon highways than upon railways, for the latter 

 usually have more competent supervision after completion. 



For the same reason, the superstructure of bridges should be 

 of the simplest kind — that which will need the least care and 

 be most easily repaired. There is no difficulty in making firm 

 spans of twenty-four feet with stringers alone, without braces 

 or truss, provided good timber of that length, fourteen inches 

 deep, can be obtained. 



For spans of forty feet and upwards, the " Howe Truss " 

 stands preeminent among wooden bridges ; and there are styles 

 of iron bridges, for spans of thirty feet and upwards, which 

 may be the cheapest in the end, if the first expense can be 

 borne. But since there is no danger of fire, we are inclined to 

 prefer the wooden bridge generally. 



We will only add that on all bridges of a considerable span, 

 signs, forbidding fast driving, should not only be put up, but, 

 what is unusual, they should be enforced; for the vibration 

 caused by rapid driving is tenfold more injurious than the same 

 loads at a walk. 



Repairs. 



A great deal of money is washed away on our highways for 

 want of constant supervision and prompt repairs. A costly 

 culvert or bridge may be saved by observing the action of the 

 water in time, and applying the necessary remedy. 



There is constantly forming in the centre of the drive a horse 

 path, and at the sides ruts, both of which prevent surface-drain- 

 age to the sides, and form excellent channels on grades for the 

 water in a rain-storm. Water stands in these at different 

 points, the surface is softened, and they are deepened more and 

 more rapidly ; for the blow of the wheel increases with the dis- 

 tance fallen. A great rain-storm comes, the road is gullied, 

 hundreds of yards of good ballast are wasted, and the charge is 

 made to the " dispensation of Providence." 



Let the road be divided into convenient sections, and a man 

 constantly employed upon each, with cart, scraper and roller, to 



