easily Recognised, from Description: 3dly Remarkable Peaks or Hills or Mountains at some distance inland but full in view from ye Coast, & which furnish a most useful kind of Surveying Marks 4thly Small Islands; or even Large ones that have Peaks at a moderate distance from the Coast. In all these Examples, what will suit the Surveyors purpose best will also be the most acceptable Land Mark & for ordinary Navigators; that is the most conspicuous. But if a choice of Objects, offer that which has the sharpest or best defined Summit ought to claim the preference as being most favorable to precision
It being difficult to follow any given Rule for the Extent of the Intervals between the fixed Points; as that must so often depend on Chance; this Particular must necessarily in many Cases be left to the Surveyors own Judgment but it must be ever in his Memory, that when such Marks do occur they ought to be no further as under than to be seen from one another; in order to answer the Purpose intended. To approach nearer to a positive Rule, they should be within half a Degree of each other at furthest & by Choice at half that distance. According to Probabilities, Cælestial Observations of both kinds; (That is the Latitude; & the Time to compare with the Time Keepers) may be expected to occur generally within the greater space & that for the Latitude still oftener. But should the Atmosphere be unfavourable to Cælestial observations, you will then content Yourself with such Data as Your Chain of Bearings or Triangles may have furnished You & proceed with your operations: correcting, if necessary the last positions by the future Observations.