JULY 11, 1912] 
NATURE 
on light and the eye, on how the eye is used in 
seeing, on the experience of sight, on action, and 
on memory. Case M. 
The “J].R.B.” Patent Adjustable Curve Ruler. 
(London: W. H. Harling.) Price 7s. 6d., 1os., 
and 12s. 6d. 
DRAUGHTSMEN and students of engineering will find 
this curve ruler a useful addition to their stock ot 
instruments. The instrument consists of a trans 
parent strip of celluloid, which may be bent 
to fit any given curve, or to pass through a series 
of plotted points. The strip is clamped to two 
slotted brass bars, one of the clamps forming a 
swivel, which may be locked at any horizontal 
angle. The slotted bars may be clamped in any 
position and at any angle to a slotted wooden bar, 
which holds the whole appliance. Two other 
slotted brass bars may be clamped to the wooden 
bar in any position, and have hooks formed at the 
outer ends; these assist in bending the celluloid 
strip into the proposed curve, and give steadiness 
to the strip. Two celluloid strips are supplied, 
one about o’05 and the other about o'1 inch in 
thickness. 
We have tested the appliance in drawing several 
curves, such as a curve to fit four points plotted 
at random, and the curves of a beam when loaded 
in various ways, and find that the maker’s claims 
are justified. Curves of large or small radii of 
curvature are easily produced, and these are even 
and regular; the appliance is adjusted very simply, 
aid retains the shape when once set, so that a 
curve may be duplicated many times. 
Post Mortems and Morbid Anatomy. By Dr. 
Theodore Shennan. Pp. xv+ 496. (London: 
Constable and Co., Ltd., 1912.) Price 18s. 
net. 
Dr. SHENNAN is to be congratulated on having 
written a treatise that gives a full and lucid 
account of the whole art of performing necropsies ; 
of studying scientifically the evidences of disease 
in the organs and tissues of the body, so far as 
these can be investigated in the post-mortem 
room; and of making permanent preparations of 
the material so obtained, either for investigation 
in the laboratory or for demonstration purposes 
in museums. 
There is, perhaps, no branch of the work of 
the practising medical man for which such a 
guide-book is so urgently needed; and this work 
is sure to prove most helpful not only to the 
practitioner who is called upon to do autopsies, 
but also to the student who is acquiring a prac- 
tical knowledge of pathology. 
Though lacking originality, either in treatment 
or in matter, it is probably the most complete and 
well-balanced text-book in English dealing with 
practical pathology. 
The illustrations are for the most part success- 
ful reproductions of photographs taken by the 
author and Mr. Norman; but some few of them 
(e.g., Fig. 79) might with advantage have been 
replaced by drawings. 
NO. 2228, vor. 89] 
| 
ERLTERS TO. THE EDITOR: 
[The Editor does not hold himself responsible for 
opinions expressed by his correspondents. Neither 
can he undertake to return, or to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of Nature. No notice is 
taken of anonymous communications.] 
Forced Vibrations. 
Witu regard to the subject of ‘‘ Forced Vibrations ” 
dealt with by Prof. Perry in his letter in Nature of 
June 27 (p. 424), Prof. E. H. Barton, of Nottingham, 
puts the matter very clearly on p. 150 of his 
“ Text-book of Sound,” 1908, where he states :—‘t The 
frequency of the impressed force to make the ampli- 
tude a maximum is lower than that natural to the 
system with friction, while the frequency of the im- 
pressed force to make the kinetic energy a maximum 
is above that natural to the system with friction, and 
equals that if friction be absent.’’ ‘‘ Moreover, the 
squares of these three frequencies form an arithmetical 
progression whose common difference is proportional 
to the square of the damping coefficient.” 
I think Prof. Perry means to convey that these 
slight eccentricities from syntonic symmetry may be 
negligible in acoustical investigations (owing to their 
being well within the limenal region of physiological 
audition), but may rise to values at which they can 
be no longer neglected in other branches of interest, 
such as the zther-acoustics of radio-telegraphy, &c. 
Prof. Perry would be doing real service by furnish- 
ing a non-mathematical explanation of these eccen- 
tricities; the graphical demonstration is a somewhat 
lengthy process. Joun L. Dunk. 
July 1. 
Mendel and Nageli. 
Mr. L. Doncaster has recently given one explana- 
tion of the strange neglect of Nageli to appreciate the 
results of Mendel. Perhaps the following footnote 
from Eimer’s ‘“‘Organic Evolution” (tr. J. T. Cun- 
ningham, 1890), p. 53, may supply another :—‘ Nageli 
in the introduction to his book speaks very severely 
of those who without any justification undertake to 
express opinions upon the origin and evolution of 
organisms. He claims this right exclusively for 
physiologists, and counts among the non-physiologists 
both Darwin and Haeckel. Against such a close 
corporation I protest.” 
The ‘‘book”’ referred to seems to be the ‘‘ Mechan- 
ische-physiologische Abstammungslehre,”’ published 
in 1884, and Mendel, who, if I remember rightly, 
was a professor of physics, is not likely to have fared 
better than Darwin or Haeckel, except for his then 
obscurity, at the hands of his distinguished corre- 
spondent. The treatment of Fleeming Jenkin’s criti- 
cisms by Darwin himself forms a pleasing contrast to 
this misplaced pontificality. H. H. O’Farre_y. 
The Avenue, Kew Gardens, July 1. 
CONGRESS OF UNIVERSITIES OF THE 
EMPIRE. 
iY an article which appeared in our issue of 
June 13 it was stated that fifty-four universi- 
ties would send delegates to this Congress. The 
nascent university of Calgary was subsequently 
excluded from the official list, on the ground that 
for the present it proposes to confine its degrees 
to agriculture. It is not difficult to imagine the 
Secretary’s feelings when he found that with the 
