Page:Philosophical Transactions - Volume 036.djvu/323

 tion. The Service they do, is to abate that Friction on the Pin's Point, which retards the horizontal Verticity; for when the Friction is divided between the horizontal Verticity, and the Librations or Tremblings (either of the two latter rolling on the Pin more speedily) the far greater Part of the Friction is spent on the Librations, or Tremblings, and consequently there is but little left to retard the horizontal Verticity. I take such a Needle to be far better for my Purpose than the common ones, which have a heavy Socket of Brass, or Steel, in the Middle, useful only to render them portable, but very detrimental in nice Experiments; because the Weight of the Socket not only blunts the Pin sooner, but also encreaseth the Friction, though the same Acuteness of the Pin should be supposed to continue. To renew the Tremblings when they began to, abate, I rarely jogged the Box on the Table, for fear of giving it (find the Needle within it) a circular Motion, which obstructs the Design: But I found it best to do it, by jogging the Table gently. When I had Occasion to turn the Needle to any other Point of the Compass, I elevated that Part of the Box which was under one End, until it rested on the Bottom, and in that Posture could turn it as I would; but before I could let down the Box again to an horizontal Position, was forced to wait till the Needle was very still, and to let down the elevated Side easily, and with a direct Motion; otherwise the Needle, as soon as both its Ends were free, would have more or less of an horizontal Motion.