320 
by an echo at Bedgebury ‘Park, the country residence of 
Mr. Beresford Hope. The sound of a woman’s voice was 
returned froma plantation of firs, situated across a valley, 
with the pitch raised an octave. The phenomenon was 
unmistakeable, although the original sound required to be 
Joud and rather high. With a man’s voice we did not 
succeed in obtaining the effect. 
At the time I had no idea that such an alteration of 
pitch had ever been observed, or was possible ; but it 
soon occurred to me that the explanation was similar to 
that which I had given of the blue of the sky a year or two 
previously (Philos. Mag., Feb. 1871). Strange to say, at 
the very time of the observation I had in my portfolio a 
mathematical investigation * of the problem of the dis- 
turbance of the waves of sound by obstacles which are 
small in all their dimensions relatively to the length of 
the sound waves. In such a case (precisely as in the 
parallel problem for sight) it appears that the reflecting, 
or rather diverting, power of the obstacle varies inversely 
as the fourth power of the wave-length. When a compo- 
site note, such as that proceeding from the human throat, 
impinges on the obstacle, its components are diverted in 
very different proportions. A group of small obstacles 
will return the first harmonic, or octave, sixteen times 
more powerfully than the fundamental. After this, it is 
not hard to understand how a wood, which may be con- 
sidered to be made up of a great number of obstacles, 
many of which, in two or three of théir dimensions, are 
small in comparison with the wave-length, returns a sound 
which appears to be raised an octave. 
The increased reflection is, of course, at the expense of 
the direct sound. If we conceive a group of small ob- 
tacles to act on a train of plane waves of sound, the etect 
will be a diffused echo, which may be heard on all sides, 
appearing to proceed from the group, and the direct waves 
which maintain their direction. If the original sound be 
composite, the diffused echo contains the higher elements 
in excessive proportion, and for the same reason the 
direct wave, being shorn of these higher elements, will ap- 
pear duller than the original sound, Itis well known that 
pure tones are liable to b2 estimated an octave too low, 
and thus it may be possible that a note in losing its har- 
monies may appear to fall an octave. 
What is here called the direct sound may itself be 
converted into an echo by regular reflection. For ex- 
ample, if a plane wall were covered with small projections , 
there would be a diffused echo, due to the projections in 
which the higher elements preponderated, and an ordi- 
nary echo, obeying the law of reflection, in which the 
wave elements would preponderate. 
I shall be much obliged if any one under whose obser- 
vations echoes of this description may happen to fall, 
would communicate particulars of them to NATURE. 
RAYLEIGH 
LEITH-ADAMS? “ FIELD AND FOREST 
RAMBLES” 
Field and Forest Rambles. By A. Leith-Adams, F.R.S. 
(Henry S. King & Co.) 
Dia: on our expressing surprise to a friend at the fact 
of his having forsaken his usual line of study for 
another of avery different character, he remarked, “ Well, 
* Since communicated in an amplified form to the Mathematical Society. 
NATURE 
[Aug. 21, 1873 
you see it does not matter much what I take up, for what- 
ever it may be, I am sure to make some discovery of 
value.” The reply was sufficient to enable anyone to form 
an idea of the results that might be expecied. He was 
an assiduous and earnest worker, but there was a certain 
deficiency in the quality of all he produced, 
Mr. Leith-Adams is an assiduous and earnest worker ; 
his opportunities in connection with his military avoca- 
tions, have been considerable, and he has used them well. 
He has already given us the results of his experience in 
India and elsewhere in his “ Wanderings of a Naturalist 
in India,” as well as in the “ Natural History and Archze- 
ology of the Nile Valley and Maltese Islands,” and in 
the work before us he takes us to New Brunswick, 
vividly portraying the beauties of its short summers and, 
the discomforts of its dreary winters. An intense love for 
natural history has led him to make careful and prolonged 
observations as to the habits of most of the animals in- 
habiting the province of which he treats, together with 
the dates and direction of migration of the numerous 
migratory birds which are there met with. He has also 
paid considerable attention to the fish, and the geology 
of the district. 
Our author, in endeavouring to obtain an accurate 
account of the past history of the native Indians of New 
Brunswick, found the task of more than ordinary diffi- 
culty, “inasmuch as, even apart from their persistent in- 
difference to treat on any subject connected with their 
past history or present condition, there would seem to be 
an absolute incapacity to comprehend the meaning of 
such inquisitiveness on the part of the interrogator.” 
Drink is the ruination of the remnant of this doomed 
race, a race so little advanced in the scale of humanity, 
that when it has disappeared, there will not be left a 
trace even of written or monumental record ; “indeed, 
were it not for implements of the chase picked up occa- 
sionally, we should have few other data to establish the 
existence of the human inhabitants of the region, previous 
to the arrival of the first European travellers.” The 
European colonist, as long as he is the possessor of the 
mens sanus in corpore sano, however, stands a better 
chance of surviving; nevertheless leprosy produces 
painful ravages among the original French settlers, on 
the north-east frontier of the province. 
No explanation is attempted of the fact quoted 
from Dr. Gilpin, that many of the wild animals, as 
the bear, racoon, and beaver, which were driven 
from their haunts on the clearing of the forests, are 
again returning to the same districts, “to cultivated 
fields instead of primitive forests, to corn and maize, in- 
stead of wild fruits and berries.” We cannot help 
thinking that this does not say much for the present 
assiduity of the farmers. 
Albinism and Melanism, the tendency for certain indi- 
viduals of a species to be white or black, is one of Mr. 
Adams’ favourite subjects, and he gives it as his opinion 
that the reason why they in the wild state do not continue 
to prop igate their peculiarity is because “the very decided 
difference as regards outward appearance would be suffi- 
cient to forbid intercourse between them and the typical 
individuals.” 
- There is a want of point in many of the author’s at- 
tempts at explanation of the various phenomena which 
