482 
NATURE 
[March 10, 1870 
The Motion of a Free Rotating Body 
I sHAatt feel obliged if, through the medium of your widely- 
circulated journal, you will allow me to point out an extraordi- 
nary mistake into which Mr. Radau has fallen, in a memoir in- 
serted in the Aznales Sctentifigues del’ Ecole Normale Supéreure 
tom. vi. 1869, in which he criticises certain of my con- 
clusions about the representation of the motion of a free 
rotating body contained in a paper published by me in the 
‘Philosophical Transactions” for 1866. In his preamble, M. 
Radau says, speaking of the theory of rotation in connection 
with the names of Poinsot, Rueb, Jacobi, and Richelot:—“ Tout 
récemment M. Sylvester a essayé d’appliquer au méme sujet des 
considérations nouvelles qui l’ont conduite a des resultats 
intéressants, 4 cOté d’autres dont l’exactitude peut étre contested.” 
Later on in his memoir M. Radau points out, and accompanies 
with yery biting (albeit toothless) criticism, the nature of his ob- 
jection, which is, in short, that I suppose Poinsot’s ellipsoid, 
under the influence of an original impulse, to roll without slip- 
ping by virtue of its friction against the plane with which it is in 
contact. My answer is, that of course Ido. Andwhynot? when I 
suppose the plane “indefinitely rough” (see p.761 of “Philosophical 
Transactions,”’ 1866), and have actually determined the friction 
and pressure at each point of the motion, so that by solving a 
maximum and minimum problem of one variable, the extreme 
value of the ratio of one of these forces to the other, or if we 
please to say so, the limiting angle of friction, or, in other words, 
the necessary degree of roughness of the plane may be analytically 
determined for every givencase. M, Radau falls into the school- 
boy blunder of making the ratio between the friction and pressure 
constant throughout the motion, confounding the actual friction with 
its limiting maximum yalue! It is, indeed, surprising that such 
a perversion of the facts of the case should have found insertion 
in a serious journal, such as that published by the Ecole Normale 
Supérieure, and I might fairly have expected from M. Radau the 
courtesy habitual with his adopted countrymen, of applying to 
me for information on anything in my paper which might have 
appeared to him obscure or erroneous, before rushing into print 
with such a mare's nest. 
But out of evil cometh good. M. Radau says :—‘‘ Mais M. Syl- 
vester va plus loin; il pense que le probléme pourrait se résoudre 
par l’observation directe du mouvement d’un ellipsoide matériel 
tournant sur un plan fixe en méme temps qu'il tournerait autour 
de son centre également fixe. On ne se figure pas facilement 
par quel artifice on fixerait le centre d’un ellipsoide matériel.” 
In a future number of your esteemed journal (as time at pre- 
sent fails me) I propose to show how, by the simplest contrivance 
in the world, a downright material top of ellipsoidal form may 
be actually made to roll, with its centre fixed, on a fixed plane 
and so exhibit to the eye the surprising spectacle of a motion 
precisely identical 77 die, as well as in its successive displace- 
ments of fosition, with that of a body, turning round a fixed 
centre, but otherwise absolutely unconstrained. 
This mode of representation, which: flashed upon my mind 
almost instantaneously when my eye first lighted upon M, Radau’s 
objections, is the compensating good to the evil of being made 
the victim (to the temporary disturbance of my beloved tran- 
quillity) of so hasty and futile a criticism as has been allowed 
insertion in the ‘‘Scientific Annals” of so great an institution as 
the Ecole Normale of Paris. 
The dureau de védaction must surely have been nodding when 
they allowed such observations, so easily refuted by turning to the 
original memoir, to pass unchallenged. It was only within the 
last few days that I received M. Radau’s paper. 
Athenzum Club, March 8 J. J. SYLVESTER 
“Engrais Complet’’ 
In England many people have no faith in simple remedies 
with simple names, such, for instance, as brimstone and treacle ; 
but make the same materials into a jam, disguise its flavour, and 
call it, say, the ‘‘ Universal Purgative Extract,” and then be- 
lievers in its efficacy will soon be reckoned by the thousand. It 
seems from a review in a recent number of NATURE, that farmers 
in France are similarly incredulous on the subject of manures 
with intelligible names, that they require what is really useful to 
be mixed with something useless, and called ‘‘ Engrais Complet,” 
before they will apply it to their land. The English idiosyncracy 
benefits a large number of patent medicine vendors, and I pre- 
sume this French variety of it benefits the manure merchants. 
Let us hope, however, that English farmers will continue to mix 
their own ‘‘Engrais Complet,” obtaining, as heretofore, their 
nitrogen from farmyard manure, guano, and nitrogenous salts ; 
their phosphorus from guano and superphosphate ; their potash 
from organic excreta and “potash salts. Under ordinary circum- 
stances, with the Norfolk four-course system, the ‘‘ Engrais 
Complet” for barley is left on the land by sheep feeding off roots 
and oil-cake ; that for roots is farmyard manure and super-phos- 
phate; that for wheat is clover roots, with a top-dressing of 
guano and salt. Clover requires little from the land but potash 
and good cultivation ; but every crop should be fed well enough 
to leave something handsome for its successor. 
Pray excuse my homely comparisons, for although a reader 
and I hope a student of NaTurRE, I am still 
ONLY A CLoD 
The Preservation of Mollusca 
THRE notice in a recent number of the use of creosote by M. 
Holbein for the preservation of mollusca, &c., leads me to re- 
mark that I have found it of great value for the preservation of 
coleoptera and other insects. The solution of creosote and 
water appears to be quite as effectual a preservative as alcohol, 
and does not harden the tissues or cause discoloration. After 
an immersion of about a week the solution should be drained 
off, and the insects placed in tins and covered with sawdust. 
Probably small reptiles, &c., could equally well be preserved in 
this way, which would save the danger of leakage and breakage 
which now ruins so many consignments. 
Cambridge. J. R. Crorcu 
Frankland and Duppa on the Action of Sodium on 
Acetic Ether 
IN their recent communication to the Royal Society, reported 
in the last number of NATURE, Messrs. Frankland and Duppa 
ascribe my not getting hydrogen by the action of sodium on the 
acetic ethers to the high pressure existing in my sealed tubes. 
How could there be a high pressure in my tubes unless I had 
first developed a large quantity of hydrogen? How then could 
it possibly be high pressure which prevented my getting any 
hydrogen? The pressure could not be due to the tension of the 
vapours of the acetic ethers, for in one experiment I employed 
acetate of amyl, which boils at 140° C., whilst I heated only 
to 100° C., and in this case, instead of getting 250 c.c. of gas, 
I got not a trace of gas. Moreover, the experiment with potas- 
sium was made in an open vessel. 
On the other hand nothing is plainer than that Frankland and 
Duppa were operating upon alcohol as well as upon acetic ether, 
and hence their hydrogen, 
London, March 3 J. ALFRED WANKLYN 
Sir W. Thomson and Geological Time 
I AM curious to know in which of his writings Sir W. Thom- 
son makes the assertion “that there was a time when the earth 
rotated too swiftly for the existence of life.” I cannot see how 
the assertion, even if it were true, could be of the least use in 
determining questions as to the length of time during which the 
earth has been habitable. Certainly it has not the slightest con- 
nection with Thomson’s argument as to the date of consolidation 
of the earth, founded on its figure and on the retardation of its 
rotation by tidal friction. Yet the assertion is distinctly ascribed 
to Thomson—/irst in the Pal/ Mall Gazette, May 3, 1869, and 
secondly in the Edinburgh Review for January last. 
If the passage quoted, or at least something resembling it, 
cannot be found in Thomson’s writings, I am anxious to know 
whether the charge is due to simple stupidity on the part of the 
critics (or critic ?), or whether it proves more ? 
G, Hi, 
Little Gull (Larus minutus) 
In the proceedings of the Royal Physical Society of Edin- 
burgh, as reported in Nature, July 17, Dr. Smith notices the 
capture of a specimen of the Little Gull (Larus minutus) in 
Scotland, and remarks that it is a rare straggler to Scotland, only 
some two or three specimens haying been previously recorded. 
Although rare in Scotland, it is by no means uncommon on the 
Yorkshire coast during the autumn and winter, and specimens 
are frequently shot during these seasons near Flamborough 
Head and along the Bridlington coast. This winter they have 
been more than usually plentiful. Myr, Richardson, of Beverley, 
