. 46 
NATURE 
[May 18, 1871 

for the mere necessities of calculation to act. All his argument, 
ifI understand it aright, depends upon the displacement being 
by fits and starts. Thus he says (NATURE, July 28, 1870), 
“The precessional force has its full effect in producing the pre- 
cession of the solid crust, the fluid xo¢ having time* to diminish 
that effect before the axis has assumed a new position ;” and 
** The friction of the fluid within, which Aas ot time to influence 
the nutation before the nutation is actually produced ;” and 
(NatuRE, May 11, 1871), ‘‘ Suppose a succession of slight hori- 
zontal pushes to be given to the poles in a continually altering 
direction, the effect will be that the revolving crust will be con- 
tinually slipping over the revolving fluid, which as not dime to 
acquire the new motions given instantaneously to the solid 
crust.” 
The leading idea in all these passages seems to me to be that 
the attractions of the sun and moon, to which precession and 
nutation are owing, act by impulses, by a succession of sharp 
pulls quickly repeated. This is truly enough the supposition 
with which mathematical calculation starts ; but the real action, 
I need not say, is a steady, continuous, though ever varying, 
pull, and it is the result of such anaction which our calculations 
in the end lead us to, by a method which enables us to get rid 
of the error necessarily involved in the approximate result which 
would follow from our first supposition. 
I cannot then help thinking that even Archdeacon Pratt has for 
once been carried away by the beauty of mathematical analysis, 
and has for the moment forgotten that the conditions which it is 
obliged to employ for its ends do not in their initial form repre- 
sent the actual conditions of nature. The explanation occurred 
to me on first reading his paper in the Philosophical Magazine, 
but seemed tome so unlikely that I shrank from putting it for- 
ward. I can, however, in no other way imagine how he can 
have come to the startling conclusion, that, if a solid shall be 
moyed by a steady, continuous pull over an interior ball of fluid, 
it can make no difference in the result, whether there is or is 
not friction between the interior of the shell and the surface of 
the fluid. Archdeacon Pratt, will, I know, if I am wrong, 
pardon my presumption and put me right. 
Barnsley, May 12 A. H. GREEN 
Graft- Hybrids 
‘ 
Pangenesis: 
EAcH person who assails this unfortunate “ provisional hypo- 
thesis ” makes the attack from his own particular point of view. 
Thus, in NATURE of last week Prof. L. S. Beale, as a micro- 
scopist, objects to it because the gemmules cannot be made evi- 
dent to the senses. From this somewhat narrow view of the 
case the atomic theory of chemistry, the undulatory theory of 
light, or the mechanical theory of heat, must all break down, for 
no one has as yet seen an ultimate atom, or an ethereal undu- 
lation. Mr. A. C. Ranyard, in the same paper, publishes a 
letter which is quite at variance with fact, for if he will turn to 
PP. 399, 391, 394, 397 in vol. i. and pp. 364 and 365 vol. ii. of 
Mr. Darwin’s work on “ The Variation of Animals and Plants 
under Domestication,” he will there find many cases given of the 
scion affecting the stock and producing intermediate forms known 
as ‘‘graft-hybrids.” Pangenesis has not yet ‘‘ received itsdeath 
blow.” R. MELDOLA 
May 13 
IN your last number Mr. Ranyard brings forward an objection 
to Mr. Darwin’s theory of Pangenesis on the ground that the 
grafting of a bud on a stock of a different species does not pro- 
duce a hybrid offspring. I am not about to defend the doctrine 
of Pangenesis, which appears to me incapable alike of proof and 
of disproof. Itis, however, a well-known fact that the stock does 
affect the scion, and zzceversé. In Prof. Henfrey’s ‘‘ Elementary 
Course of Botany” (Dr. Masters’s edition) he says, “A certain 
amount of physiological influence of the stock over the scion is 
shown to exist by such facts of horticultural experience as that 
the fruit of the pear is smaller and more highly coloured when 
‘worked on’ the quince and medlar than when grafted on 
pear-stocks, and is earlier when worked on the mountain-ash.” 
The well-known instances of the communication of variegation 
from the scion to the stock in Aéut/on, recorded by Prof. 
Morren and others, are considered cases of contagious disease ; 
Lut what is the theory of contagion but that the blood or other 
* IT have taken the liberty of italicising those expressions which seem to 
me of vital importance to the argument in these quotations, 

‘*fluid” of an animal or plant is affected by emanations, call 
them “gemmules” or what you will, from another individual ? 
The same writer records an instance which he considers well 
authenticated of the production of the hybrid Cytiss Adam: by 
the grafting of C. purpureus on C. laburnum. 
ALFRED W. BENNETT 
The Rev. Mr. Highton and Thermodynamics 
You are cruelly kind to Mr. Highton in giving him space to 
develop his absurdities. 
His new remarks on Joule, like his earlier ones on a paper by 
Sir W. Thomson, simply show that Ae does not understand what 
he ventures to criticise. Of course, what Joule now says is pre- 
cisely what he said a quarter of a century ago, with the simple 
difference that it is put ina somewhat more popular form. 
No one who has taken the trouble to understand the experi- 
mental facés and the elementary reasoning of which the Laws 
of Thermodynamics are the condensed expre-sion, has any more 
doubt of their truth than of the truth of Newton’s Laws of 
Motion. They are, perhaps, a little harder to understand ; but 
the proof is of the same nature, and already almost of the same 
extent, in the newer science as in the older one. 
Ihave not seen the Review of Popular Science referred to by 
Mr. Highton, but I hope (for the credit of that journal) that he 
misconceives its statements as he does those of Joule. ; 
Your “ first reviewer” (or rather précis-writer) of his article, 
whoever he may be, certainly gives him no encouragement in 
the number for Jan. 19, whatever may have been the effect of 
my treatment of his not singular case. 
Your REVIEWER 
On the Radial Appearance of the Corona 
WOULD an indefinitely extending solar atmosphere, if its 
existence could be proved, be in itself sufficient to explain the 
appearance of the solar corona? Should we not still have to 
explain the apparent radiation which is so distinctly part of the 
phenomenon ?—If the light or heat of the sun which radiates 
symmetrically outwards as from a point at its centre be the cause 
of the illumination, surely the figure of the corona would bear 
some relation to the figure of the atmosphere or medium on 
which the light or heat acts? Yet I think I may say that it is 
quite impossible to conceive a medium so distributed and arranged 
as to form rays such as those seen in thecorona. If the recent 
photographs had not shown beyond a doubt that this irregular 
radiating appearance belongs to the corona and the neighbour- 
hood of the sun,* it would have gone a long way to prove that 
the corona is at least partly due to the earth’s atmosphere or 
mere optical effect. But, as it is, I think this radiation clearly 
proves that the corona cannot be due to the direct action of the 
light and heat of the sun on any surrounding matter. In fact, I 
cannot conceive an atmosphere the character of which varies in 
a radial manner, however rapidly either its nature or density 
may vary with the distance from the surface of the sun. If, 
instead of an atmosphere, we try to conceive a ring of meteors, 
still the radial gaps so clearly marked on the photographs pre- 
sent insurmountable difficulty. This, moreover, is impossible on 
other grounds. It is impossible that there can be an almost 
homogeneous mass of meteoric matter circulating round the sun 
in the torm of an outersphere, and if it circulated im the ecliptic 
or any other plane, it would present the appearance of Satum’s 
belt, whereas the corona appears altovether different trom this, 
and cannot possibly bea film of light in any plane but that of the 
sun’s limb. 
Nor can these radial rifts be of the nature of shadow. For 
the shadow which anything like a sun spot would produce in a 
misty atmosphere must be conical, the vertex of the cone being 
outwards, so that the edges of the shadow would approach each 
other instead of receding as they do. Moreover, such a shadow 
would still be seen through a great extent of illuminated so ar atmos 
sphere, and therefore be only partial or faint, whereas the ri/ts are 
so dark and definite as to imply a total absence of coronal light ; 
this must be the case unless the rifts or gaps in the spherical 
envelope extended right across the sphere from front to back, 
and we know that there is no obstruction on the surface of the 
sun that could cast such an extensive shadow. 
What, then, does this radiated appearance show the corona to 
be? I think that it proves that the corona is an emission 
either of illuminated matter or of an action iluminaung matter, 

* Has this yet been established —Ep. 

