‘March 9, 1871] 

Quinary Music 
Mr. JEVONS, in his interesting paper on the Limits of Numeri- 
cal Discrimination (NATURE, Feb. 9), asserts in support of his 
views (Rees Cyc, “‘ Rhythm”) that ‘‘no musicians have yet been 
found capable of performing ” quinary music. 
I have never found the slightest difficulty, nor can I conceive 
any, either in performing or inventing music subdivided into five 
isochronous measures, 7.¢., with an accent recurring on every 
fifth unit of measure; nor do I see anything to justify his doubt 
that the ear can grasp divisions of 6, 8, 9, without regrouping 
them into smaller periods; as amongst skilled musicians there 
exists no doubt whatever about the continuous reading of those 
larger groups, without even a suggestion of such subdivision ; 
and it would be easy to multiply quotations from the best writers 
of passages whose only correct performance and reception by the 
“isteners would be entirely destroyed by such a sub-grouping as 
Mr. Jevons seems to think necessary. 
Apropos :—I greatly doubt whether the question of musical time 
is at all pertinent to the subject of numerical discrimination, as 
an instantaneous conception; the latter being a synchronous 
mental act, while the former is altogether consecutive in its 
operation, in which every group, however small, is only a 
sequence of units, JosEPH MULLEN 
a8, Synge Street, Dublin, Feb. 14 

The Power of Numerical Discrimination 
In an article with this title in a recent number of NATURE, 
Mr. W. S. Jevons offered the results of some ingenious experi- 
ments he had been making to determine how many objects the 
human mind could count by an instantaneous and apparently 
single act of attention. He comes to the conclusionthat the 
power of his mind was limited to something less than five. 
If it were Prof. Jevons’ purpose to ascertain the number of 
objects he could count within an interval too short for more than 
a single conscious act of attention, his experiments were, doubt- 
less, conclusive, at least to him ; but if he sought through them 
to prove that he or any other person could fix his attention upon 
more than one object at a time, I fancy he commits the mistake 
attributed to the Royal Society in puzzling over the question put 
them by Charles I. about the effect of throwing a shrimp into a 
pail full of water. He is trying to account for a phenomenon 
that never occurred and which can never occur. 
Prof. Dugald Stewart, in his work on the ‘‘ Philosophy of the 
Human Mind”* has proved very clearly, it seems to me, that 
the attention is never fixed upon two points or objects at the same 
time, but that it passes from one to another in certain cases, as 
in playing upon musical instruments, in feats of jugglery, &c., so 
rapidly as to seem to be instantaneous. ; ; j 
In addition to what Prof. Stewart has said upon this subject, 
permit me to ask how it is any more possible for the attention to 
be fixed on two beans at one time than for two beans to be in the 
same place at the same time? The argument that could demon- 
strate the absurdity of the last of these propositions would 
demonstrate the absurdity of the first. 
If Mr. Jevons will try to look at both eyes at once of the first 
person he talks with, he will find that one of the eyes seems 
more distinct to him than the other, and every effort he may 
make to equilibriate his attention will only result in changing it 
from one to the other. k 
If he is talking with great earnestness, or in a way to 
make his interlocutor very anxious to divine his meaning and 
penetrate or anticipate the expression of his inner thoughts, 
he will notice that his interlocutor’s eyes seem to be running 
from one of his own eyes to the other, as if in hopes of getting 
from one some disclosures not made by the other. This would 
not be done if both eyes could be seen simultaneously. 
Mr. Jevons seemed to see five beans, because he was able to 
run over and count five in the minimum of conscious time. 
I think there is no authority for saying that there is any period 
of conscious time necessary for any purely mental operation. To 
the mind itself, or the spirit of a man, there is neither space nor 
time. There are incidents of our material organisation which 
limit our capacity to notice and remember mental operations, 
but not the operations themselves. Therefore the rapidity with 
which the attention is transferred from one word to another in 
reading, or from one key to another of a piano when played by 
* Works of Dugald Stewart. Edited by Sir William Hamilton. Art. 
“* Attention.” 
NATURE 

367 
ee 

4 master, authorises no presumption whatever that his attention 
is ever fixed upon more than one key at a time, while all the 
presumptions are against the possibility of any person’s attention 
ever being in two places at the same moment. JaeBs 
Berlin, March 4 
Eozoén Canadense 
ON a careful consideration of Dr. Dawson’s reply to the ob- 
jections urged by me against the supposed organic nature of 
Eozo6n Canadense, I confess my inability to see that one single 
fact is brought forward calculated to shake the position of those 
who regard it as a purely mineral production. 
In opposition to all previously received opinion, Dr. Dawson 
would now confine Eozoén to the Laurentian period. I am glad 
to accept this as evidence that its Canadian discoverers begin to 
feel the force of the ‘‘ difficulties” I have stated, and instead of 
ignoring them, make a genuine and divec¢ attempt to meet them. 
Though Dr. Hunt now doubts the accuracy of the observations 
which refer the Skye ophite to the Lias, he has elsewhere as 
good as admitted that it is not confined to the Laurentian 
period.* Giimbel has also determined it for Cambrian meta- 
morphic rocks in the Fichtelgebirge, Bavaria, and Rupert Jones 
and Sandford for rocks of the Lower Silurian period in Conne- 
mara, as pointed out by Mr. Kinahan in his letter in NATURE 
(No. 66), The Tudor specimen, it is also considered, may belong 
to the Cambrian or Potsdam group. This, to say the least, is 
somewhat contradictory. 
The determination of the age of the Skye ophite I am willing to 
leave Dr. Hunt to settle with Professors King and Rowney, merely 
remarking that both McCulloch and Geikie, as independent ob- 
servers not looking for evidence in support of a theory, declare 
the rock to be of the Liassic age. 
The lengthy disputes as to what is to be considered Eozoon 
and what is not, are most amusing. When each disputant takes 
up a different position and shifts it as occasion requires, how is 
he to be met? And is this not of itself sufficient primé facte 
evidence of weakness such as to warrant a suspension of judgment 
on the part of those—and their number is great—who have 
accepted the ‘‘ fossil” only on the strength of eminent names and 
reiterated assurances ? 
As far as I can make out, the whole positive evidence is now 
narrowed down to the determination of what is and what is not 
the true “nummuline layer.” A reference to the published 
figures and descriptions gives no information by which we may 
detect any difference between the ‘‘nummuline layer” of the 
Skye ophite and that of the typical Canadian specimens. Thus, 
then, until Dr. Dawson points out the difference, this objection 
cannot be said to be “wholly irrelevant.” To aver, without 
proof, that when the characteristic structure occurs in an unlooked- 
for position, that it is an zzzfiative form, or, on the contrary, to 
assume it to be a /oss7/ when discovered elsewhere, is easy, but 
does not tend to carry conviction to the unbiassed mind. To do 
this, we require distinct and ample evidence. The Eozoén before 
referred to as discovered by Mr. Sandford in the Connemara 
ophite, and “verified” by Rupert Jones,+ belongs, according to 
Murchison, to the Lower Silurian age.t The discovery, it 
appears, had at the time induced Sir Roderick to class this rock 
as Laurentian, but shortly afterwards, purely from stratigraphical 
considerations, he pronounced it to be Lower Silurian.§ Here, 
again, we have a discordance with the views of Dr. Dawson ; 
are we, then, to throw away such independent testimony, and say 
that the unfortunate Eozoén “ Hibernicum” is an iitative form, 
or, are we to consider the veteran geologist wrong, and the Con- 
nemara marble Laurentian ? 
It is now seen that all the theories which attempt to meet the 
objections I have stated are in conflict—which then is right ? 
As regards the Tudor specimen, which, it is thought, I have 
too summarily ‘‘ disposed” of, I would observe that it was 
brought forward with great é/atas a conclusive answer to all 
objections founded on the comparison of the structures of Eozoén 
with the forms of fibrous, dendritic, or concretionary minerals. 
The reasons why I dissent from this view are: 1st. The ‘‘chambers” 
are admittedly ‘‘more continuous and wider in proportion to the 
septa” than specimens found elsewhere. They are, in fact, little 
more than an aggregation of concentric plates or perhaps only 
bands, and according to the figure do not show the true segments. _ 
2nd, The microscope reveals ‘‘for the most part merely traces 
* Silliman’s American Fournal, July 1870 
+ Geological Magazine, vol. ii. p. 87. 
} Ibid. p. 147. § Ibid, p. 97. 
