The Artizan . te themselves to the use of their base, and try the measure-ments on objects at various distances likely to be met with in practice; fromthese they would obtain a series of differences of the angles at A and B, whichwould guide them correctly to judge of the distance, while the experience theywould thus acquire would tend to give them confidence in the use of the tried a measurement of this kind on an esplanade on the Mersey with a and a ship in the stream; the angle C B D read 40° 40, and the angleCAD 39° 30, difference 1° 10, indicating, for the purposes of
The Artizan . te themselves to the use of their base, and try the measure-ments on objects at various distances likely to be met with in practice; fromthese they would obtain a series of differences of the angles at A and B, whichwould guide them correctly to judge of the distance, while the experience theywould thus acquire would tend to give them confidence in the use of the tried a measurement of this kind on an esplanade on the Mersey with a and a ship in the stream; the angle C B D read 40° 40, and the angleCAD 39° 30, difference 1° 10, indicating, for the purposes of navigation, a verynear object. After a little practice, I believe that all that the officer in commandwould want would be to hear the value of the first angle called over to him, andthe number of minutes it differed from the second, in the same way that thefathoms and half fathoms are now given him by the man casting the lead. Whenthe number of minutes approached to 60, the object would be dangerously near;. but if they were reported to be one-third, or a quarter of that amount, then thedistance from the landmark would be known to be safe. The accuracy of this method of obtaining a distance while the ship is steamingor sailing depends on two things :—First, the reading oft the angles at A and B,to which the junior officers of a ship are usually well trained. Second, to readingthem by signal at the same second of time. The importance of this conditionwill at once be seen, when it is considered that the point A arrives at the placeB has occupied in five or ten seconds of time, depending on the length of the baseline and speed of the ship. I submit the above mode of measuring distances from on shipboard as one offacile application, and which requires only what is already to he found in everysea-going vessel. Of its value, the trial by various hands must be the ultimateguide for coming to a correct conclusion. I have proposed above a single base line for each ship, commencing
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