To have the exclusive right, at all times, to supply the city with gas or other light, and such persons, partnerships and corporations therein as may desire the same, at such prices as may be agreed upon; and also to have, at all times, the unrestricted right to make, erect and maintain the necessary buildings, machinery and apparatus for manufacturing and distributing the same; or, in territory not supplied with light, to make contracts with and authorize any person, company or association so to do, and to give such person, company or association the privilege of supplying gas or other light, as aforesaid, for any length of time, not exceeding ten years.