72 
Witchell, and that is with regard to mimicry. Un- 
doubtedly several birds are ready to mimic sounds which 
they hear about them, but it does not follow that every 
point of resemblance in the songs of two species is due 
to mimicry; it is quite as likely to be accidental. For 
instance, it seems to us fanciful to trace the origin of part 
of the song of a thrush in the following way : 
“The ‘ kreeow’ was given in the deliberate manner of 
the crow ; the ‘ whillillill’ was similar to the note of the 
wryneck ; while the ‘tewy’ was clearly the call-note of 
the chiffchaff.” 
In another place we read : 
“The nightingale is sometimes inclined to mimic, and 
one of its strains, a rapid ‘slip slip slip’ prolonged, is 
much like the sound made by the young perching 
nightingale when the parent is feeding it.” 
It seems curious that the nightingale should mimic the 
young birds when they are not yet hatched, for, in spite 
of the fact that nightingales are heard singing in mid- 
June, we do not believe that they generally sing after 
their young are hatched; and Mr. Witchell gives no 
evidence that the birds he heard were not delayed in 
their nesting owing to the destruction of their first 
nest. 
Mr. Witchell is well known as a specialist in bird-song, 
and many of his observations could not be made without 
a carefully trained ear ; so his book cannot fail to be of 
interest. We are doubtful as to the amount of help it 
would give to a novice wishing to become familiar with 
the various cries of birds ; but it gives a fuller description 
of these cries than is generally to be found in ornitho- 
logical works, and suggests many points which are worth 
further investigation. jaly (On 120 
OUR BOOK SHELF. 
Psychologische Untersuchungen tiber das Lesen. 
Benno Erdmann and Raymond Dodge. Pp. viii + 360. 
(Halle, 1898.) 
The Story of the Mind. By J. M. Baldwin. 
(London: George Newnes, Ltd., 1899.) 
PAINSTAKING records of psychological experiments are, 
as a rule, not the most entertaining form of literature. 
Yet an exception must certainly be allowed in the case of 
the work of Drs. Erdmann and Dodge, which is no less 
distinguished by literary charm than by the thoroughness 
and completeness of the investigations it records. The 
greater part of this admirable work is devoted toa careful 
and, in the judgment of the present reviewer, unanswer- 
able refutation of the opinion which since Wernicke has 
been current among German pathologists, that in normal 
reading the letters are spelt out separately, one after 
another. By a series of elaborate experiments the authors 
seem to establish beyond a doubt that our apprehension 
of a written text takes place exclusively during the pauses 
between the movements of the eye along the lines, that 
six to seven letters can be clearly perceived during each 
such pause, and finally that a short word of not more 
than four letters can be read off in less time than a single 
letter. In the later chapters Cattell’s well-known experi- 
ments on reaction-times for written symbols are submitted 
to asearching criticism ; and it is shown from the absence, 
under normal conditions, of conflicting optical suggestions 
or of conscious sensory-motor “feelings of innervation ” 
that no element of “ discrimination ” or “ selection ” enters 
into our ordinary apprehension of the meaning of the 
symbol. As this means that simple apprehension is oz 
NO. 1547, VOL. 60] 
Pp. 263. 
NATURE 
[JUNE 22, 1899 
“discrimination” of any kind, the result is an important 
one, and may be commended to the attention of those 
psychologists who still talk glibly of “discrimination” as 
the essential feature in perception. Altogether the book 
is a model of what a psychological monograph should be, 
clear, well-arranged, and most accurate. 
Prof. Baldwin’s little book is a valuable addition to the 
series in which it appears, and should awaken the interest 
of not a few intelligent general readers outside the little 
world of psychologists by profession. It is remarkable 
that he should have been able in so few pages to intro- 
duce his readers to almost every side of psychology. 
The most excellent feature of the book is probably the 
abundant illustration, from Prof. Baldwin’s own re- 
searches, of the meaning and nature of psychologica} 
experiment. If one were in a fault-finding mood one 
might, perhaps, complain that the curious attack upon 
the teaching of language at p. 222 is both exaggerated 
and irrelevant, and that the concluding chapter on “ The 
Genius and his Environment” is hardly definite enough 
in its results to justify its being reprinted from the popular 
magazine in which, no doubt, it has made a previous 
appearance. A. E. TAYLOR. 
Sewage Analysis. By J. Alfred Wanklyn and W. J. 
Cooper. Yp. xiv +220. (London: Kegan Paul, 
Trench, Triibner, and Co., Ltd., 1899.) 
Sewer Design. By H. N. Ogden, C.E. Pp. viii + 234. 
(New York: John Wiley and Sons. London: Chap- 
man and Hall, Ltd., 1899.) 
THE first of these two volumes is described as “a 
practical treatise of the examination of sewage and 
effluents from sewage.” Many practical hints on the 
analysis and treatment of sewage are given; and the 
collection of original papers printed as an appendix 
contains useful notes and explanations on various 
analytical processes in chemistry. The object of the 
book is, however, stated to be to bring about a re- 
formation in the analysis of sewage, and to point 
the way to its proper disposal. Apparently one of the 
chief reforms required, according to Mr. Wanklyn, is to 
induce chemists using the ammonia process of water 
analysis to express the readings of albuminoid ammonia 
in terms of parts per million, instead of parts per 100,000 
and grains per gallon. But other reforms are urged ; 
and as Mr. Wanklyn claims that ‘“‘ In some respects the 
Opportunities enjoyed by my colleague and myself are 
absolutely unique,” and remarks that “the severance of 
all relations with the London Chemical Society has 
operated to our advantage,” the volume evidently con- 
tains criticisms and conclusions upon which a difference 
of opinion may be permitted. 
Prof. Ogden’s volume contains a course of lectures 
given in the College of Civil Engineering, Cornell 
University. It shows how the subject of sewer design 
may be dealt with scientifically, and therefore practically. 
Much scattered material upon points which have to be 
considered when preparing the design and making the 
plans for a system of sewers in a city, has been brought 
together by the author. Sanitary engineers will find 
the volume as serviceable for reference as students of 
sanitary engineering will find it helpful as a text-book. 
The Hygiene of the Mouth, a Guide to the Prevention 
and Control of Dental Diseases. By R. Denison 
Pedley, F.R.C.S. Edin., L.D.S. Eng. Pp. 93. (Lon- 
don: J. P. Segg and Co.) 
THE importance of taking care of the teeth of children 
cannot be too strongly emphasised or too widely under- 
stood. In this volume the author describes the measures 
to be adopted for the prevention of dental diseases in 
adult life, the progress and treatment of dental caries, 
and some of the consequences of neglect of the teeth. 
The facts contained in the book should be known to 
every parent. 
“ 
