March 3, 1870] 
NATURE 
459 
does not only consider the differences of the vibration-rates of 
pairs of over-tones, but inquires also whether they are w/in 
beating distance of each other. In the former case alone can 
they become a source of dissonance. The interval of an octave 
is a perfect consonance, because every partial-tone of the higher 
sound coincides with one of those of the lower; and thus any 
slight deviation in pitch will produce beats between each adjacent 
pair. 
The interval of a fourth is less consonant than that of a /7/7i 
—not, as Prof. Tyndall represents it, on account of its 66 beats 
which, but a single octave below that in which he has placed it, 
ought to become the worst possible dissonance—but because the 
second partial-tone of the higher sound comes within beating 
distance (a whole tone) of the third partial-tone of the lower, as 
shown on the staye— 
when the fundamental tones are written in minims, and the 
over-tones in crotchets. 
I may as well notice that a diagram given by Helmholtz * to 
illustrate various degrees of dissonance, and copied by Prof. 
Tyndall, + is accompanied by the latter with an explanation 
giving a wrong idea of its meaning. The diagram, as ex- 
plained by its author, is intended to represent to the eye the 
degrees of roughness attaching to intervals greater than one 
octave, and not exceeding two. Prof. Tyndall having evidently 
missed the remark of Helmholtz {that C’, wot 7ts octave C’, 
**is to be the constant fundamental tone of all the intervals,” 
has represented the diagram as ‘‘beginning with the unison 
C”—C"” and going up to the octave intead of beginning 
with the octave C’—C” and going up to the double octave 
C’—C”. The diagram as it stands in Prof. Tyndall’s lecture 
is calculated to convey an impression as unlike its author’s 
meaning as it is contrary to fact. 
Trinity College, Cambridge, Feb. 26. SrpLry TAYLOR 
The Valuation of Liquid Town Sewage 
TuHouGu I consider it highly unbecoming for one member of 
a committee, charged with an important inquiry, to criticise 
publicly and in a controversial manner, views expressed by 
another member of that committee in regard to the subject it 
has to investigate, still some of the remarks made by Mr. Hope 
at the Society of Arts last Wednesday seem so unmistakeably to 
refer to the article which appeared in NATURE on the 23rd 
December last, that I feel constrained, as the writer of that 
article, to reply to them. The statement objected to by Mr. Hope 
was an expression, not of individual opinion, but of the fact— 
long accepted as beyond question—that the practical value of 
liquid town sewage as manure, that is to say, its value to the 
farmer, cannot be computed so/e/y from the amount of manure 
material it may contain, and that, in forming such an estimate, the 
positive element afforded by chemical analysis must be controlled 
by the negative element introduced by extreme dilution, and 
varying under different local circumstances. This fact has been 
recognised by authorities too numerous to name, and so deci- 
sively, that Mr. Hope’s assertion as to the value of the ammonia 
in sewage being affected only in a very minor degree by the 
amount of water mixed with it, seems to have no other merit 
than that of being ‘‘ sensational.” I am at a loss to conceive 
what ground Mr. Hope could have for objecting to 
the statement that ‘‘it is a great mistake, and likely to 
prove a very ruinous one,” to estimate the value of dilute sewage 
by calculation solely from the amount of manure material it may 
contain. Yet this is what Mr. Hope characterises as a ‘‘ strange 
paradox.” Why it has puzzled him, as he admits, I will not 
stop to inquire; but I must protest against his representing 
“the obligation of applying water to crops at all times of the 
year, whether they want it or not,” as having been one of the 
reasons given for the statement he objects to. In doing that he 
has at least fallen into a great error, and he has at the same time 
evaded the point to which attention was directed in the article, 
viz., the agricultural difficulty attending the ‘‘continuous daily 
application of sewage to land.” That is a difficulty not to be 
disposed of ex cathedra—it would obtain whether the land des- 
* The second on page 292, t Page 208, } Page 201. 
tined to receive sewage were under crops or lying fallow. In 
the one case the application of sewage might be inadmissible 
during great part of the year; in the other case the land under 
fallow would be unproductive meanwhile. Indeed the need for 
applying sewage to fallow land, which Mr. Hope seems to sug- 
gest, would enhance the difficulty of disposing of sewage by irri- 
gation, since it would involve the want of a still larger area of 
land for its reception, day by day throughout the year. Sucha 
mode of application might well necessitate an area of twenty-five 
acres for every 100 persons, and that necessity, if it existed, would 
be, I imagine, a very serious matterin the case of many towns. 
I will not attempt to occupy your space by considering the 
question whether leaving land under fallow is to be regarded as 
a feature of progress in agriculture; nor will I venture an opinion 
as to whether water be the ‘‘best dung-cart,” further than to 
express my surprise that, in regard to this question, Mr. Hope 
should have recourse to a chemist’s opinion while declaring that 
its decision is not within the province of the chemists. 
The case put by Mr. Hope, with an air of anticipatory triumph, 
of a man who applies to his land an excessive and useless amount 
of manure, seems to me an exact parallel to the use of liquid 
sewage in many instances, for whether it be the fancy or the 
folly of the farmer, or some other circumstance, which impels 
him to use manure in such a way that the possible effect cannot 
come up to the amount of manure applied, I should imagine it 
to be obvious that, to the user, the value of the manure must be 
gauged by the practical effect likely to be realised. I should 
expect this view to be appreciated even by the bucolic intellect 
which Mr. Hope seems disposed to contemn. 
As stated by the chairman at the Society of Arts meeting, the 
views held by Mr. Hope on the general subject of town refuse 
are clear and precise. There is no doubt what those views are, 
but it is not my intention to enter upon any discussion of them. 
At the same time, as a member of the British Association Com- 
mittee, and having individually entertained the expectation that 
Mr. Hope’s co-operation would be of material service in the in- 
quiry it has to make, I cannot avoid expressing my regret that 
he declares himself a partisan of one particular solution of the 
town-refuse problem. There are, probably, few questions of the 
day which demand more careful and impartial consideration than 
this one-—few that less admit of being dealt with for the promo- 
tion of a project at any price. For my own part, therefore, I 
deem it a misfortune that the value of Mr. Hope’s well-known 
ability and extensive knowledge of this subject should be limited 
by his avowal of a foregone conclusion. 
February 28. 
BENJAMIN H. Pau 
Weeds in Newly Turned Ground 
From a recent address of Mr. Bentham, the President of the 
Linnzean Society, it would appear to be still uncertain whether 
the weeds which appear spontaneously on ground which has 
been newly turned over, spring from seeds hidden in the 
ground, or from seeds accidentally carried on to the new sur- 
face. Could not this question be decided by a simple experi- 
ment, namely, by turning over some suitable ground and 
covering parts of it by gardener’s glass frames, so as to prevent 
the importation of any seeds? So far as the weeds are the 
same both within and without the frames, it is certain that they 
must spring from seeds previously contained in the earth. It is 
true that there will be a difference of temperature beneath the 
glass and in the open air, but it would not prevent us from 
learning what seeds are really contained in the earth. A frame 
covered with fine muslin would serve instead of glass if the 
muslin be fine enough to prevent the passage of any seeds, 
Je 
Skeleton Lectures on Science 
I HoPE you will allow me, through your valuable pages, to 
suggest what I have no doubt would be a most powerful and 
successful means for promoting scientific knowledge throughout 
the length and breadth of the land. There are hundreds of 
persons with the desire and a sufficient taste and general know- 
ledge of science, who now devote themselves to penny readings, 
who would be too glad to give popular lectures on scientific sub- 
jects, if they could only be aided by skelefon lectures, and the 
loan, on moderate terms, of simple apparatus, diagrams, &c., to 
illustrate the same. It certainly would well remunerate any 
scientific instrument maker to loan out apparatus for such 
lectures. 
Skeleton sermons are enormously in request, why not skeleton 
| lectures on science ? Vive 1p 
