The mariners magazine, or, Sturmy's mathematical and practical arts containing the description and use of the scale of scales, it being a mathematical ruler, that resolves most mathematical conclusions, and likewise the making and use of the crostaff, quadrant, and the quadrat, nocturnals, and other most useful instruments for all artists and navigators : the art of navigation, resolved geometrically, instrumentally, and by calculation, and by that late excellent invention of logarithms, in the three principal kinds of sailing : with new tables of the longitude and latitude of the most eminent places ... : together with a discourse of the practick part of navigation ..., a new way of surveying land ..., the art of gauging all sorts of vessels ..., the art of dialling by a gnomical scale ... : whereunto is annexed, an abridgment of the penalties and forfeitures, by acts of parliaments appointed, relating to the customs and navigation : also a compendium of fortification, both geometrically and instrumentally / by Capt. Samuel Sturmy.

By the Traverse-Scale.

Extend the Compasses from the Point made good in the last summing up, to the number of Leagues or Miles Difference of Latitude by Observation, and by Dead Rec∣koning, in the Line of Numbers; the same Distance will reach from some Points from the East and West, to the Difference of East or West.

As for Example.

Extend the Compasses from 2 Points and a little more (which was the Sum of the Course made good the 31 of March) unto 2 7/10 Leagues, which is 8 min. or there∣abouts in the Line of Numbers; the same Extent will reach from 6 Points to 1 1/10 Leagues and something more in the Line of Numbers, and that is the increasing Westerly. You may also with the same Extent correct the Distance, if you put one Foot at W or 100 in the Line of Numbers, the other will reach to the Distance 2 9/10 Leagues corre∣cted by Observation, as you see I have done in the Journal. So you see, That understand∣ing perfectly the Use of the Traverse-Scale, you may do the same, and more readily, as Mr. Norwood doth with his Table, to every Degree and Minute of the Quadrant, without sensible Error.

Now this Difference being found, I add therefore and put down in the South Co∣lumn the Difference 2 70/100 Leagues, and the West Column 1 16/100 Leagues, and under Distance 2 9/10 Leagues: Now the same corrected is by observation 130 9/10 Leagues, Distance 120 10/100 Leag. Southing and Westing 52 Leag. 8 min. substracted from the Dead Latitude, make 38 deg. 30 min. the true corrected Latitude according to observa∣tion:

Then I sum up the first Sums of the 28 of March, and this Sum corrected 31 of March together, and you have the Distance 278 Leagues,* 1.1 Difference of Latitude 256 84/100 Leagues, and Departure 108 64/100 Leagues, and by the Rules before-given 256 8/10 Leagues Southing, and 108 6/10 Leagues Westing; and with the Difference in Me∣ridional Leagues 364 7/10 Leag. I find the Difference of Longitude in Leagues 154 ••/10 Leagues, converted into deg. and min. is 7 deg. 43 min.

In like manner, upon the third of April I should be in Latitude 32 deg. 19 min. but by very good observation, I find the Ship in the Latitude 32 deg. 30 min. that is, not so much Southerly by 11 minutes: therefore to correct it by Observation, I put under Distance 3 9/10 Leagues, and in the South Column 3 66/100 Leagues, and in the East 1 50/100 Leagues, and under Dead Latitude 11 min. I substract the corrected Difference of Distance out of the Sum over it, and likewise the corrected Difference in the North Column out of the Sum in the South, and likewise the East out of the West Column, and add the 11 min. to the Dead Latitude, and then you have the Sum corrected; but if there be any Current, you may set it down, and allow for it, and note it down, as is that Example following the first of April to the third, and by your Traverse-Scale presently find how much the Current hath set you to the Eastward.

But if your Course be neer the East and West,* 1.2 it is sufficient to correct it in Lati∣tude only, as in the Example of the 12th and 13th of May; for in that Case the Longitude cannot be corrected but from some further ground. Now to set down this Reckoning upon the Plain Chart, or common Sea-Chart, it is needless and unnecessary: The better way is to set down every one of the Sums as they are corrected by Observa∣tion, in the same manner as you are directed in the latter end of the third Chapter of this Book; and so by the total Sums of the Difference of Latitude and Departure from the first Meridian, or Latitude and Meridian-distance, you may set it down on your Draught or Chart as often as you please with ease.

Now to set off every Sum corrected in Degrees of Latitude and Leagues of Longi∣tude, you have a Scale of Leagues or Miles for that very purpose, and Directions how to do it, in the ninth Chapter of this Book: But if you are desirous to set down your Reckoning in a Mercator or Mr. Wright's Chart, on in the Polar Chart, you have in the 12th and 13th, or last two Columns of your Journal, the substance and principal scope of your Reckoning set down as often as you sum up or correct your Reckoning: name∣ly, your Latitude and Longitude; which whensoever you have a desire to set down in the foresaid Chart, or any other graduated Chart, with Degrees of Longitude and La∣titude, you may readily do it.

As for Example. Suppose I would set down the Plat of the aforesaid Journal from the 25th of March to the 13th of May, I find the Latitude against the 25th of March 51 deg. 20 min. and the Latitude of the Barbadoes 13 deg. 10 min. and the Difference of Longitude 52 deg. 35 min. Therefore in the Latitude of 13 deg. 10 min. I draw or point out an occult Parallel, and reckon 52 deg. 35 min. from the Island Lundy towards the West: I draw by that Longitude an occult Meridian;* 1.3 the Intersection of this Meridian with the foresaid Parallel is the Point representing Bar∣badoes, or the Place of the Ship; and the like is to be understood of any of the other: And so I put down in the General Chart of Mercator the 8 Points of the Ship's Place, 1 a, 2 b, 3 c, 4 d, 5 e, 6 f, 7 g, 8 h, as there you may see. This form of keep∣ing a Reckoning is the most fit and agreeable of all others as I have seen or heard of, to all sorts of Charts, Maps, or the Globe it self, and to all kinds and ways of Sailing whatsoever.

Notes

• * 1.1

  This is because I find my self to the Northward, that is, less to the Southward by 11 m. than by Dead Reckon∣ing, & therefore less to the West∣ward 1 50/100 Leag. or so much to the Eastward, by reason my Course is in the S. W. Quarter, it must be corre∣cted in the con∣trary Quarter.
• * 1.2

  In sailing East and West, you have a Rule in Probl. 7. of sail∣ing by Mercator or Mr. Wright's Chart.
• * 1.3

  I hope this way will find good acceptation with the ingenious Mariner or Artist.