 "Whereas great mischiefs have arisen by the outrageous and unlawful behaviour of labourers and others employed on railroads [sic], canals, and other public works, by reason whereof the appointment of special constables is often necessary for keeping the peace, and for the protection of the inhabitants and security of the property in the neighbourhood of such public works, whereby great expenses have been cast upon the public rates of counties and other districts chargeable with such expenses