1301.] Deſcription of Mr. Logan's Spire-Buoy. 23

borne at an angle of 45? with the perpendicular depth, were fixed in a manner ſimilar to the floating beacons at Ply mouth, by a continuation of the axis through the centre of the baſe. For, in this poſition, the a&ing power of the ſea, or the velocity and preſſure of the ſtream, become, in a great meaſure, ſpent, without effect, on the convexity of the buoy or on the inclined plane of its baſe, by which the actual force towards breaking the chain or ſinking the buoy is greatly diminiſhed. s

Hence proceed the diferent cauſes of the inutility of the pre- ſent Channel-buoy in the oblique poſition, and its frequent fatal conſequences in the deſtruction of ſhipping; for, in this po- ſition, it is liable to become inviſible éven by reflection either of the ſun or moon, or by a low haze upon the ſurface of the ſea not exceeding three or four feet high, which frequently happen on the ſea-coaſt, when it is clear every where elſe. The buoy is thus liable to be run foul of, to be dragged from its ſtation, or finally deſtroyed by the ſhips paſſing over it, or otherwiſe the ſhips themſelves are deſtroyed, or in the moſt imminent danger of being ſo by miſling it.

Theſe objections are obviated by the improvements in the Spire-Buoy, fig. 2, 3+.

A. The verticle axis, or perpendicular ſtaff, fixed in the centre of the pyramidic cone, from the baſe to the vertex.

B. C.D. The flag(as in fig. 2,) or a weather-cone(as in fig. 3,) made of wind-boards, moving on pivots, let into the iron collars B and D, and into the horizontal frame C; by which their edges are always preſented to the wind, ſo as to admit its paſſing free without effect: but, at the ſame time, to exhibit in any direct bearing or poſition, to a ſhip at ſea, the ſolid form of a double cone.

E. F. The cap and vertex of the cone, bound by two ſtrong iron hoops, and through which the ſtaff paſſes to the centre of the baſe-line or extreme diameter.

G. H. The ftream-hoop, or fream-angle of the conic pyra- mid; otherwiſe called the ſtream-cirèéle.

I. K. The lower circumference of the baſe under water z otherwiſe called the lower baſe.

L. M. The keel through which are fixed. the eye-bolts, ſuſpending the ſtream-circle.

N. The iron roller and frame, at the end of the mooring= chain, which traverſe to and from the centre of the ſpan or baſe-chain, in proportion to the quantity of action imprefled.

N. O. Part of the mooring-chain, at the half-tide angle, borne at full ſtreſs; which deſcends by the gravitation or motion

+ Fig. 2 is ſeen fideways; fig. 3 in front,