Mr. Ivory on the Theory of the Equilibrium of Fluids. 439 
have been thus particularized, on the Pheasant’s progress in 
her voyage commencing at Sierra Leone, and terminating at 
New York, it may be seen, that she was indebted to their aid 
on the balance of the whole account, and in the direction of 
her course from port to port, not less than 1600 geographical 
miles, the whole distance being under 9000 miles ; affording a 
very striking exemplification of the importance of a correct 
knowledge of the currents of the ocean to persons engaged in 
its navigation ; and consequently of the value of the informa- 
tion, in the acquisition and arrangement of which Major Ren- 
nell has passed the later years of his most useful life. The 
publication of the charts of the currents in the most frequented 
parts of the ocean, which he has prepared with his accustomed 
and well-known indefatigable assiduity, and strict adherence 
to the evidence of facts,—as soon as he shall deem them suf- 
ficiently complete for the public guidance,—will be a most im- 
portant service rendered to practical navigation. 
LXIII. Notice relating to the Theory of the Equilibrium of 
Fluids. By J. Ivory, Esq. M.A. F.RB.S. 
To the Editor of the Philosophical Magazine and Journal. 
Sir, 
S I find that what I have written on the equilibrium of 
fluids is misrepresented on some occasions, I must beg 
leaye to occupy a small space in your Journal, in stating cor- 
rectly the points I have endeavoured to establish. 
In the Philosophical Transactions for 1824, and in the pages 
of your Journal, I have treated specially of a homogeneous 
fluid. The equilibrium in this case, according to what is laid 
down in all the books, is contained in a single law; namely, 
that the gravitation at the outer surface be directed inward at 
right angles to that surface, at the same time that the diffe- 
rential equation is integrable without supposing any relation 
between the coordinates. ‘That this is a correct account of 
the received theory I need only cite the Mécanique Celeste, 
Liv. 1™¢. Nos. 17 and 34. Liv. 3™¢. No. 22. No condition is 
required with respect to the interior of the fluid, and the rea- 
son is expressly given. Comme on peut dans Vinterieur dune 
masse homogene, prendre telles couches que Von veut, pouP 
couches de densité constante; la seconde des deux conditions pre- 
cedentes de Vequilibre, est toujours satisfaite, et il suffit pour 
Vequilibre, que la premiere soit remplie ; cest-a-dire que la re- 
sultante 
