Section 4
SEC. 4. The gas manufactured shall be produced by the use of Manufacture of coal, crude oil, or water, or any combination of these elements, but the grantee shall have the right and authority to modify, improve, and "change such method in such manner as the progress of science and improvements in the manufacture of gas may make reasonable and proper: Provided, however, That the service shall be in with the laws and ordinances now in force, or that hereafter may be in force.