Page:Philosophical Transactions - Volume 004.djvu/58

 the Suns Refraction, which is inconsiderable, and therefore needs not to betaken notice of.

Give to each of the Watches a name or a mark, as A. B. C; and before you set saile, set them to the time observ'd by the Sun in the place, where you are, and whence you are departing, allowing for the Æquation of the day, whereon you make your Observation; Which day you are to note, if the Watches be not well adjusted; otherwise it is not necessary.

Then afterwards being at Sea, and desiring to know the Longitude of the place where you are, that is, how many degrees the Meridian of that place is more Easterly or Westerly, than the Meridian of that place where you did set the Watches; you must observe by the Sun or Stars, what time of the day it is, as precisely as is possible, and note at the same time, to what hour, minutes and sec. the Watches doe point (which time, if the Watches be not set to the right measure, is by the known daily difference to he adjusted,) adding thereunto the Æquation of the present day, which gives you the time of the day, shew'd by the Sun, at the place where the Watches were set: And if this time of the day be the same with that, observ'd where you are, then you are under the same Meridian with the place, where the Watches were set by the Sun; but if the time of the day, observ'd where you are, be greater than that shew'd by the Watches, you may be assur'd, that you are come under a more Easterly Meridian; and if less you are come under a more Westerly, And counting for every hour of difference of time, 15 degrees of Longitude, and for every minute, 15. minutes or ¼ of a degree, you shall then know, how many degrees, minutes, &c. the said Meridians doe differ from one another.

E. g. Suppose, the Watches A. B. C. were set at the place, whence you parted, on the 20 of February, to the time of day observ'd by the Sun, abating the Æquaiion of the 20th of Febr. (viz 2 min, 28, sec.) and suppose that the Watch A. be Rh