Section 886, R.S. 4687, related to employment of officers of Army and Navy in the work of surveying the coast of the United States. Section 887, R.S. 4688; acts Aug. 30, 1890, ch. 837, 1, 26 Stat. 382; June 5, 1920, ch. 235, 1, 41 Stat. 929, provided for allowance for subsistence to officers of Army and Navy while employed on coast survey service.