460 PHILOSOPHICAL TRANSACTIONS. [aNNO 1773, 



tinued by those who are desirous to have it done, and are sufficiently acquainted 

 with what follows. Mr, Jones first gives the organical description of the lines 

 of the 2d kind, or curves of the 1st kind, in the following manner. 



The Description of Lines of the Second Kind. 



Let the right lines at>, aq, be drawn on a plane, at any inclination to each other. See pi. 7 , fig, 

 13, J 4, 15. In AD, AQ, take ao, am, of any given magnitude, and draw mn parallel to ad. On 

 the points a, a, let two rulers ap, op, revolve, and cut mn, aq, in n and q, so that aqi be every 

 where equal to m n . Then shall the intersection p of the rulers describe lines of the 2d kind, or curves 

 of the first kind. 



Where the right line Aa, is the first, or transverse diameter. The point c, bisecting the diameter 

 Afl, is the centre. The right line pd, drawTi parallel to aq, is the ordinate to tlie diameter a«. 

 The part ad, or CD, of the diameter, is the absciss, when reckoned to begin from a to c, or fi-om 

 c to A. The right line b6 drawn from the centre c parallel to the ordinate pd, and terminated in 

 the curve, is called the 2d, or conjugate diameter. Those diameters to which the ordinates are per- 

 pendicular, are called the axes. And ah is the parameter to the diameter \a. 



From this description, Mr. Jones then proceeds to deduce the several nu- 

 merous properties of these lines, in short algebraical expressions or equations: 

 but these, in the present advanced state of the conic sections, may well be spared 

 on this occasion. 



XXXVII. An Essay, towards Elucidating the History of the Sea Anemonies.* 

 By Abbe Dicquemare, Prof, of Exper. Philos., &c. at Havre de Grace. 

 Translated from the French, p. 36 1. 



There is great confusion in the descriptions which naturalists have given of 

 these animals, and no less in the names bestowed upon, and the divisions or 

 classes assigned to them. Some have called them sea-nettle, urticae marinae, 

 though these animals are not prickly, as some of the wandering nettles are. 

 Other writers have called them sea anemonies. The sea anemonies found on 

 the coast of the Havre seem to constitute 3 different species. Those here put in 

 the first class, because in certain positions they resemble most the flower known 

 by the name of anemone, cling or adhere to rocks and stones, and are often 

 found in the holes that chance to be in them, and seem to like the surface of the 

 water. The outer shape of the body of this animal, when it contracts itself, is 

 much like a truncated cone, pi. 8, fig. 1,-f- with its basis fixed and strongly 

 clinging to the rock. Its upper part is terminated with a hollow. This cone is 

 often perpendicular to its basis; sometimes it lies in an oblique position to it, or 

 the basis spreads itself irregularly; so that from a round, it alters to an elliptical 

 shape. Sometimes it imitates pretty exactly the inclosing out-leaves of anemo- 



* The Sea Anemonies belong to the genus Actinia, and are by no means uncommon on most of 

 the European coasts. 

 , t This seems to be the Actinia Mesembryanthtmum of Ellis. 



