A Briefe Introduction to Geography Part 4

First vpon the Globe it is most easie. With a payre of Compa.s.ses take the distance betweene any two places howsoever scituated vpon the Globe, and apply the distance so taken to the aequator, & see how many degrees it takes vp; those degrees turned into miles shew the distance of the two citties on from another.

Vpon vniuersall mapps theire is a little more difficulty in finding the distance of places which here must bee considered in a threefold difference of scituation:

1 Of Lat.i.tude only.

2 Of Longitude only.

3 Of Lat.i.tude and Longitude together.

1 If the two places differ only in Lat.i.tude, and lie vnder the same Meridian if the places lie both on one side of the aequator, the differences of the lat.i.tudes: or the summe of both lat.i.tudes added together, if one place lie North and another South, being turned into Miles giues the true distance.

2 If the places differ only in Longitude, and lie both vnder one paralell of lat.i.tude the difference of longitude turned into miles proportionably accordinge to the lat.i.tude of the paralell, giues the true distance.

3 The distance of places differing both in lat.i.tude and longitude may thus bee found out, first let there bee drawne a semicircle vpon a right diameter noted with (_ABCD_) whereof (_D_) shall bee the Center. The greater this Semi-circle is made, so much the more easie will bee the operation; because the degrees will bee larger. Then this Semicircle being drawne, and accordingly devided, imagine that by the helpe of it, you desire to find out the distance betwixt London and Ierusalem, which Citties are knowne to differ both in longitude & lat.i.tude. Now, that the true distance betwixt these two places may be found out, you must first substract the lesser longitude out of the greater, so shall you find the differences of their longitudes, which is 47.

degrees. Then reckon that difference vp[~o] the Semi-circle, beginning at (_A_) & so proceed to (_B_;) & at the end of that difference, make a marke with the leter (_E_) vnto which point by your ruler, let a right line be drawne from (_D_) the center of the Semi circle. This being in this sort performed, let the lesser lat.i.tude be sought out which in 32 degrees, in the fore said semicircle, beginning your accompt from the point (_E_) and so proceede towards (_B_), and at the end of the lesser lat.i.tude let another point be marked out with the letter (_G_), from which point, let there be drawen a perpendicular line which may fall with right Angles vpon the former line drawen from (_D_) to (_E_), and where it chanceth to fall, there marke out a point with the letter (_H_): This being performed let the greater lat.i.tude which is 51 degrees 32 minuts, be sought out in the semicircle beginning to reckon from (_A_) towards (_B_) and at the end of that lat.i.tude set another point signed out by the letter (_I_) from whence let there be drawen another perpendicular line that may fall with right angles vpon the diameter (_AC_): & here marke out a point with the letter (_K_), this done take with your compa.s.se the distance betwixt (_K_) and (_H_) which distance you must set downe vpon the diameter (_AC_) placeing the one foot of your compa.s.se vpon (_K_) and the other towards the center (_D_) and there marke out a point with the letter (_L_); then with your compa.s.se take the shorter perpendicular line (_GH_,) and apply that widenesse vpon the longer perpendicular line (_IK_,) placing the one foote of your compa.s.se at (_I_,) which is the bounds of the greater lat.i.tude, and extend the other towards (_K_), and there make a point at (_M_), then with your compa.s.se take the distance betwixt (_L_) and (_M_), and apply the same to the semicircle. Placing the one foot of your compa.s.se in (_A_) and the other towards (_B_), & there marke out a point with the letter (_N_), now the number of degrees comprehended betwixt (_A_) and (_N_) will expresse the true distance of the two places, which will bee found to be 39 degrees: which being multiplied by 60. and so converted into miles according to the former rules, will produce 2340. which is the distance of the said places.

FINIS.