STOP Early Journal Content on JSTOR, Free to Anyone in the World This article is one of nearly 500,000 scholarly works digitized and made freely available to everyone in the world by JSTOR. Known as the Early Journal Content, this set of works include research articles, news, letters, and other writings published in more than 200 of the oldest leading academic journals. The works date from the mid-seventeenth to the early twentieth centuries. We encourage people to read and share the Early Journal Content openly and to tell others that this resource exists. People may post this content online or redistribute in any way for non-commercial purposes. Read more about Early Journal Content at http://about.jstor.org/participate-jstor/individuals/early- journal-content . JSTOR is a digital library of academic journals, books, and primary source objects. JSTOR helps people discover, use, and build upon a wide range of content through a powerful research and teaching platform, and preserves this content for future generations. JSTOR is part of ITHAKA, a not-for-profit organization that also includes Ithaka S+R and Portico. For more information about JSTOR, please contact support@jstor.org. * * Fkilo* TratuwsS. N°4$fi. --I [ «JJ] I. ^ *f#, into - De- ,74,z " grees, £ Minutes, and -~ Minutes, by a Diagonal Scale j and the £ Pegrees,. and \ Mi- nutes, and -fa Minutes, counted for Degrees,, Minutes, and £ Minutes. A By is a Telefcope, three or four Feet long, fixt on the Edge of that Brafs Plate. G, is a Speculum, fixt on the faid Brafs Plate per- pendicularly, as near as may be to the Obje&-glafs of the Telefcope, fo as to be inclined 4 $ Pegrees to the Axis of the Telefcope, and intercept half the Ljght Which would otherwise come through the Telefcope to the Eye. C T>, is a moveable Index, turning about the Centre C, and, wirh its fiducial Edge, (hewing the Degree^, Minutes, and \ Minutes, on the- Li/mb of the Brafs Plate PjQj the Centre C, muft be Qver-againft the Middle of the Speculum G, H, is another Speculum,. parallel to the former, vyhen the fiducial Edge of the Index falls on ood 00' 00' 7 5 fo that the fame Star may 'then appear through X the the Telefcope, in one and the fame Place, both by the direct Rays and by the reflex'd ones -, but If the Index be turned, the Star fhall appear in two Places, whofe Diftance is {hewed, on the Brafs Limb, by the Index. By this Inftrument, the Diftance of the Moon from any Fixt Star is thus obferved : View the Star through the Perfpicil by the direft Light, and the Moon by the Reflext (or on the contrary) ; and turn the Index till the Star touch the Limb of , the Moon, and the Index (hall (hew upon the Brafs Limb of the Inftru- ment, the Diftance of the Star from the Limb of the Moon ; and though the Inftrument (hake, by the Mo- tion of your Ship at Sea, yet the Moon and Star will move together, as if they did really touch one another in the Heavens; fo that an Obfervation may be made • as exactly at Sea as at Land. And by the fame Inftrument, may be obferved, cxa&ly, the Altitudes of the Moon and Stars, by bringing them to the Horizon ; and thereby the Lati- tude, and Times of Obfervations, may be determined more exactly than by the Ways now in Ufe. In the Time of the Obfervation, if the Inftrument move angularly about the Axis of the Telefcope, the Star will move in a Tangent of the Moon's Limb, or of the Horizon; but the Obfervation may notwith- ftanding be made exa&ly, by noting when the Line, defcribed by the Star, is a Tangent to the Moon's Limb, or to the Horizon. To make the Inftrument ufeful, the Telefcope ought to take in a large Angle : And to make the Obferva- tion true, let the Star touch the Moon's Limb, not on the Outfide of the Limb, but on the Infidc. II. The