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.

PROBL. I. How to find the Logarithmes of any Number under 1000.

EVery Page in the Table of Logarithmes is divided into 11 Columns; the first of which Columns, having the Letter N at the Head thereof, are all Numbers suc∣cessively continued from 1 to 1000: So that to find the Logarithmes of any Num∣ber,

is no more but to find the Number in the first Column, and in the second Co∣lumn you shall have the Logerithme answering thereunto.

Example. Let the Number given be 415, and if it is required to find the Loga∣rithme thereof, in the Table of Logorithmes, in the first Column thereof, under the Letter N, I find the Number 415, and right against it in the next Column I find 618048, which is the Logarithme of 415. In the same manner you may find the Logarithme under 1000; as the Logarithme of 506 is 704151, and the Logarithme of 900 is 954243, &c.

But here is to be noted, That before every Logarithme must be placed his proper Characteristick; viz. If the Number consist but of one Figure, as all Numbers un∣der 10, then the Characteristick is 0; if the Number consist of two Figures, as all Numbers between 10 and 100, then the Characteristick is 1; if the Number consist of three Figures, as all Numbers betwixt 100 and 1000, then the Characteristick is 2; and if the Number consist of four Figures, as all between 1000 and 10000, the Characteristick must be 3. In brief, the Characteristick of any Logarithme must con∣sist of an Unit less than the given Number consisteth of Di••its or Places: And by ob∣serving this Rule, the Logarithme of 415 will be 2.618048, and the Logarithme of 506 is 2.704151, and the Logarithme of 900 is 2.954243, &c.