720 PHILOSOPHICAL TRANSACTIONS. [aNNO ITjQ. 



much more than we find they do ; and the variation of gravity in different lati- 

 tudes, in going from the equator to the poles, as found by pendulums, would 

 not be near so regular as it has been found by experiment to be. ;. 



4. The density of the superficial parts of the earth, being however sufficient 

 to produce sensible deflections in the plumb-lines of astronomical instruments, 

 will thus cause apparent inequalities in the mensurations of degrees in the me- 

 ridian ; and therefore it becomes a matter of great importance to chuse those 

 places for measuring degrees, where the irregular attractions of the elevated parts 

 may be small, or in some measure compensate one another ; or else it will be 

 necessary to make allowance for their effects, which cannot but be a work, of 

 great difficulty, and perhaps liable to great uncertainty. 



After all, it is to be wished, that other experiments of the like kind with this 

 were made in various places, attended with different circumstances. We seldom 

 acquire full satisfaction from a single experiment on any subject. Some may 

 doubt, whether the density of the matter near the surface of the earth may not 

 be subject to considerable variation ; though perhaps, taking large masses 

 together, the density may be more uniform than is commonly imagined, except 

 in hills that have been volcanos. The mountain Schehallien however bears not 

 any appearance of having ever been in that state ; it being extremely solid and 

 dense, and seemingly composed of an entire rock. New observations on the at- 

 traction of other hills, would tend to procure us satisfaction in these points. 

 But whatever experiments of this kind be made hereafter, let it be always grate- 

 fully remembered, that the world is indebted, for the first satisfactory one, to 

 the learned zeal of the r. s. supported by the munificence of George the Third. 



Tables are then added of all the zenith distances of the several fixed stars, 

 that were observed, at the two observatories, from which was deduced the pre- 

 ceding quantity of the celestial arc, answering to the geographical distance h&- 

 tw^en the^aarallelsof latitude passing through the two observatories. 



■v)iear«L ^^° °^ '^"^ sixty-fifth volume of the original. 



/. On the Nature of the Gorgonia ; thai it is a real Marine Animal, and not of 



a Mixed Nature, between Animal and Vegetable. By John Ellis, Esq. 



M. D., F. R. S. In a Letter to Daniel Solander, M. D., F. R. S. Anno 17 7 6, 



Vol. LXFI. 



It was your particular request, before you went to the South Seas, that I 

 should continue my researches into the formation and growth of Zoophytes, more 

 particularly of those formerly called Ceratophytons, now Grorgoniae ; and known 

 in English by the name of sea-fa;is, sea-feathers, and sea- whips, to which class 



