doimi a Ship’s Trade (m Sea Charts. S79 
It will follow from this, that the true course of the ship will 
be one continued unbroken line ; but the dead reckoning course 
will be a series of terminated lines running off from the successive 
true places. The advantages of this method are these : In the 
first place, it will be evident that as long as there is no current,, 
tlie true and dead reckoning places will coincide, and there will be 
but one line on the chart ; but the instant that a current begins 
to act, the true and dead reckoning places will be different, and 
consequently the lines will separate : and whenever the current 
ceases, there will again be but one line. These distinctions 
catch the attention at once ; but the plan has this farther great 
advantage, that the line joining the dead reckoning place and the 
true place, at any given hour, will express correctly the direc- 
tion, and the set of the current, in the interval between the mo- 
ment under consideration, and the instant of the last preceding 
observation. 
It is useful, in practice, to have the line expressing the true 
course distinguished in some way from those marking the dead 
reckoning courses: one may be a strong black line, the others dot- 
ted lines ; or when a chart is much covered with tracks, it is useful 
to use differently coloured lines. It is sometimes satisfactory to 
join the dead reckoning places and the true places by arrows, 
and then rub out the whole of the tracks ; so that all which is es- 
sential, as far as currents are concerned, is retained, while all 
that is not, and which might tend to confuse, is removed. 
When one or more days elapse without an observation, the 
dead reckoning track may be carried on till an observation be 
obtained, and then the dead reckoning place and the true place 
at that; instant being noted, a knowledge of the strength and 
direction of the current during the interval, is at once afforded. 
On the chart, Plate VIII. which accompanies this notice, there 
are two tracks of ships off the Cape of Good Hope, which will 
render what has been said quite clear. 
It may be said that there is a fallacy in supposing tlie 
places, as laid down from chronometers and lunar observations, 
to be the true places : to which I would answer, that although 
it is not strictly the true place, it is generally not far from 
it ; and for all practical purposes it may be so considered, be- 
cause the object is, to ascertain the difference between the true 
