344 
NATURE 
[May 27, 1915 

orders cannot be accounted for by assuming that the 
atoms in the salt crystal are made up of single rings 
of electrons, or by assuming a uniform volume dis- 
tribution of the electrons in spheres. A distribution 
which fits Bragg’s data acceptably is an arrangement 
of the electrons in equally-spaced, concentric rings, 
each ring having the same number of electrons, and 
the diameter of the outer ring being about o-7 of the 
distance between the successive planes of atoms. 
If, as D. L. Webster assumes (Phys. Rev., vol. v., 
p. 238, 1915) the trains of waves of the primary beam 
of X-rays are short compared with the distance which 
the rays penetrate the crystal, certain corrections have 
to be applied to the experimental data, and on this 
assumption it can be shown that the average distance 
of the electrons from the centre of the atom is small 
compared with the distance between the atoms. 
Experiments are now in progress to test the validity 
of Webster’s assumption and to determine more 
accurately the rate of variation of the intensity of 
the reflected beam with the order. It is hoped that 
it will be possible in this manner to obtain more 
definite information concerning the distribution of the 
electrons in the atoms. ArtHur H. Comprow. 
Palmer Physical Laboratory, Princeton, N.J., 
April 29. 
I wave to thank the Editor for his kindness in 
allowing me to see Mr. Compton’s letter. I believe 
Mr. Compton is right in ascribing the rapid “decline 
in the intensities of the X-ray spectra as we proceed 
to higher orders to the fact that the atom should 
not be treated as a point, but as a distribution of 
electrons in space; if this is so, we may hope to 
determine this distributiv:: when we have measured 
the relative intensities accurately and have learnt to 
interpret them. This hypothesis and its consequences 
were discussed by me in the Bakerian lecture given 
before the Royal Society in March last. As only 
short notices of the lecture have yet appeared in 
print, I may mention one or two of the points then 
raised. 
It seems convenient to imagine a periodic distribu- 
tion of density such as occurs in a crystal to be 
analysed by Fourier’s series, in a manner suggested 
by previous work of Rayleigh, Schuster, or A. B. 
Porter (Phil. Mag., January, 1906, p. 154). Each har- 
monic distribution of density is responsible for one 
order of reflection. The results of measurements with 
calcite seem to show that the intensity (not the ampli 
tude) of the reflection by a ‘*harmonic reflector’ is 
proportional to the amplitude of the harmonic distribu- 
tion of density; that is to say, that the intensity of 
the reflection is proportional to the mass of the 
reflector. It is necessary to explain, not only why the 
intensities of the various orders fall off approximately 
as the inverse square of the number of the order, 
but also why atom-bearing planes give intensities 
whose reflections are proportional to the squares of 
the distances separating the planes. It appears that 
both laws follow from the same hypothesis, viz. that 
which supposes the reflecting electrons to be distri- 
buted in space through the volume of the atom, and 
which imagines much overlapping to take place— 
atoms of one plane being thrust far into the interstices 
of the next. 
Experiment seems to fit in with these ideas. Prob- 
ably, however, it is necessary to take account also of 
a difference in the distribution in different atoms. For 
example, certain results seem to indieate that the 
sulphur atom is more concentrated than the zinc. 
The University, Leeds. W. Hi. Brace. 
NO. 2378, VOL. 95] 


Early Figures of the Remora. 
As remarked by Dr. Albert Gtnther, in his article 
on the history of the Remora (‘‘On the History of 
the Echeneis,” Ann. Mag. Nat. Hist., 1860, ser. 3, 
vol v., p. 386), ‘‘there is scarcely a fish of the exist- 
ence of which the ancients have been equally certain, 
and which has so much occupied their imagination 
. as the Echeneis of the Greeks or Remora of 
the Latins.’’ Also, the same author continues, ‘* there 
is scarcely a group of fishes . . . which has been so 
little comparatively treated, and which has experienced 
a similar splitting up into nominal species.”’ 
The ancient legends associated with this fish, from 
which it derives its name, signifying ‘* ship-holder,” 
persisted until well into modern times; and what is 
probably the earliest illustration of the Remora in 
printed books shows several of these creatures engaged 
in arresting the progress of a vessel. The curious 
woodcut referred to is found in that late fifteenth- 
century work known as ‘Hortus  Sanitatis,” the 
author or compiler of which styles himself Johannes 
von Cube, or Cuba, by some thought to have been a 

punning pseudonym for Dr. Wonnecken, town 
“~< a = 
—] 
471 HBS z 
% lt = Ss 
Pay E 2 s 
Jia “a Ay 
is ) 
Fic. 1.—Earliest known printed figure of the Remora, 
from the ‘‘ Hortus Sanitatis” of J. von Cube. 
physician of Frankfort. First printed about 1490, 
the work enjoyed considerable popularity, as is proved 
by its having passed through several editions. A copy 
of the design representing the Remora, taken from 
the 1536 edition, is shown in Fig. 1. 
The next oldest illustration of the Remora appeared 
in a book, or perhaps a map, printed during the first 
half of the sixteenth century, and was copied by 
Conrad Gesner in book iv. of his “ Historie 
Animalium,” published in 1558. It is shown in 
Fig 2. The same figure, more or less modified, re- 
appears in various seventeenth-century works on 
natural history, as, for example, those of Nierem- 
berg, Aldrovandi, Jonston, Ruysch, and others. 
Search for the original after which Gesner’s figure 
was copied has proved unavailing; but the subject of 
the sketch, and also the verbal description, are trace- 
able to the account of a West Indian species of sucls- 
ing-fish, the first printed description of which is found 
in the ‘‘ Libretto” of Peter Martyr of Anghera, pub- 
lished in 1504, and reprinted three years later in the 
collection of voyages known as ‘‘Paesi novamente 
Trovati.” 


