The great advantage of having a road perfectly exposed to the action of the sun and wind will be more accurately conceived by referring to writers of science on evaporation. Dr. Hailey states that one-tenth of an inch of the surface of the sea is raised per diem in vapour. He also says that the winds lick up the water somewhat faster than it exhales by the heat of the sun. Other writers say the dissipation of moisture is much accelerated by the agency of sweeping winds, the effects being sometimes augmented five to ten times. Trees are particularly injurious by not allowing the sun and wind to have free action on the surface of roads producing evaporation. Besides the benefit which a road receives from its drying rapidly by an open exposure to the atmosphere, there is another of great importance, namely, that of affording to horses the advantage of free respiration; for it is well known that the powers of a horse to perform work with ease, particularly when moving rapidly, depends upon the quantity of cool and fresh air that he can pass through his lungs. If the cause of horses tiring or becoming ill under their work be carefully examined into, it will often be found that it is not their muscles or limbs that fail them, but their wind; and therefore, it is particularly important to have a road so circumstanced that a horse may on all parts of it have the benefit of a free current of air. [147] No person can put up hoards or scaffolds in the streets without first obtaining the consent of the urban authority, _vide_ sections 144 and 149 of the Public Health Act 1875. Many towns also have private improvement Acts with very binding clauses on this subject, empowering the surveyor to demand a fee for a licence to erect a hoarding, and empowering him to remove these after notice, &c. [148] This is scarcely ever feasible, or of the slightest use if done. [149] Mr. Cooper states that “a tall chimney will rock 1 inch in a moderate wind, and even to an extent of ¹⁄₈th of an inch at a distance of only 16 feet up from its base, and yet be safe.” (_Vide_ ‘Minutes of Proceedings of the Institution of Civil Engineers,’ vol. xxvii. p. 100.) [150] Whilst this work was in the press the terrible disaster arising from the falling of an immense chimney shaft at Bradford took place, the result of which was the death of upwards of forty persons and great destruction of property. CHAPTER XVII. IMPROVEMENT OF PRIVATE STREETS. Prior to the passing of the Public Health Act 1875 the improvement of private roads and streets was dealt with under section 69 of the Public Health Act 1848, but the clause under which the town surveyor now works is that which is so well known as the 150th section of the Public Health Act 1875, and is as follows: