58 Survey of Oyster Bars, Somerset County, Md. 



chart marking the position of the three landmarks selected. The center of the hub of 

 the protractor will indicate on the chart the actual position of the buoy, and if the 

 point thus obtained does not coincide with the true position of the corner of the bound- 

 ary as given on the chart, the surveyor can proceed to locate the buoy correctly by 

 reversing the operation. This is done by placing the center point of the hub of the 

 protractor over the corner of the boundary in question and measuring on the chart the 

 two adjacent protractor angles between the three selected landmarks. One of the 

 angles thus obtained is set on the sextant and the boat moved about until the two land- 

 marks are shown by the sextant to subtend the same angle obtained from the pro- 

 tractor. The second angle is then placed on the sextant and the same operation gone 

 through, and so on, first using one angle on the sextant then the other until a point is 

 reached where both observed sextant angles are practically identical with the pro 

 tractor angles. The point thus located is the desired one and the buoy can be placed to 

 mark the true position of the corner of the boundary in question. 



If the engineer possesses two sextants and a protractor, this problem is far easier 

 of solution, as the two angles can be set off on separate sextants and the observer can 

 quickly find the desired point where they agree with the protractor angles by using one 

 sextant after the other without the need of resetting either. 



If there are two observers, two sextants, and a protractor, it can be seen that the 

 best conditions for both rapid and accurate hydrographic locations of points are attained; 

 in fact, this is the method by which the buoys at the corners of the boundaries were 

 originally placed by the hydrographic engineer to the Commission. 



.(3) Magnetic bearings from offshore. — This method of fixing a position on water is 

 a simple and well-known one in navigation. It is available to anyone having a boat 

 compass and will be of special use to the State fishery force in investigating cases where 

 buoys are supposed to have been moved for illegal purposes. 



In the case where a buoy is supposed to have been moved from its true position 

 the observer takes compass bearings to the three landmarks given in the last column of 

 the tables opposite the boundary corner in question. These bearings are then corrected 

 for the local declination," and if the results agree with the published bearings the buoy 

 is correctly located. 



In the case where the buoy is not in its correct position, or has disappeared alto- 

 gether, the desired point can be determined by maneuvering the vessel until the cor- 

 rected bearings agree with the ones in the tabular descriptions, when the buoy can be 

 anchored in its proper location. 



In the case where the landmarks for which the bearings are published have been 

 destroyed or washed away, any landmarks whose positions are indicated on the charts 

 can be used by getting their bearings directly from the chart by parallel rulers or a pro- 

 tractor and then applying them in the same manner as the ones published in, the tables. 



(4) Magnetic bearings from shore. — This method will be of special value to engineers 

 having an ordinary surveyor's compass. The compass can be set over the point mark 

 ing a " triangulation station" on shore, the name of which is given in the last column 

 opposite the "corner" in question. The instrument is then set at the corresponding 



"The mean magnetic variation of Somerset County for 1908 was 5 30' west of north and increasing 

 at the rate of 3' yearly. 



