342 
NATURE 
[May 27, 1915 


mentioned. The majority of young people are left 
to find things out for themselves, or from their 
equally blind or ignorant fellows. The danger of 
this method, especially in the early days after 
puberty, when bad habits formed are so difficult to 
eradicate subsequently, is recognised by educa- 
tionists, but, as a rule, nothing is done to counter- 
act the evil. Miss March shows that instruction 
on this most important matter can be given with- 
out any loss of delicacy, by making biology a 
school subject, and by practically studying the 
development of certain plants and animals. She 
also very rightly urges that there should be 
greater frankness and confidence between parents 
and their children, and that reticence on the part 
of either should be discouraged. Great pains have 
been taken to make the biological statements 
clear and accurate. 
The book is addressed to parents and teachers, 
not to the children themselves. There are many 
subjects dealt with, such as prostitution and 
sexual diseases, which it is quite unnecessary for 
mere children to understand; the evils of the 
world will become apparent quite soon enough, 
and we feel sure that these evils would be less 
if only young men and maidens were, at an early 
stage, taught to understand and respect their own 
bodies. It is because Miss March has made a 
successful attempt to induce parents to realise 
their responsibilities that we welcome her book. 
Vian Seetls 
The Theory of Measurements. By Dr. A. de 
Forest Palmer. Pp. xi+248. (New York: 
McGraw-Hill Book Co. ; London: Hill Publish- 
ing Co., Ltd., 1912.) Price 2.50 dollars or 
tos. 6d. net. 
Tue author has prepared this treatise on the 
theory of measurements to meet the needs of 
students in engineering and advanced physics, and 
to impress on them the importance of realising 
the significance and the precision of the measure- 
ments made. 
In the first seven chapters the general principles 
of measurement, the nature and distribution of 
errors, and the methods which are employed to 
arrive at the most probable result, are set forth 
clearly. 
Measurements of various kinds are discussed, 
to show the importance of determining the pre- 
cision of the result obtained if the operation is to 
be of any real value. 
A general discussion of errors, which is very 
clearly stated, leads up to the method of least 
squares, and throughout the subject numerical 
examples are worked out so that the student may 
see for himself the treatment of measurements 
and the errors which arise. 
The second half of the book is devoted to a 
general discussion of the precision of measure- 
ments, to which the earlier chapters have formed 
a suitable introduction. It is in this portion that 
the author’s aim to lead the student to test 
systematically the results which he obtains is 
best seen, and the guidance given for the ade- , 
NO. 2378, VOL. 95| 

quate discussion of completed observations and of 
| proposed measurements is most valuable. 
The whole subject is clearly and comprehensively 
set forth, and is illustrated by numerous examples 
of physical measurements, which are fully worked 
out. The book is to be recommended to the 
student as a useful guide to the systematic dis- 
cussion of measurements and the determination of 
their adequacy. M. 

EEBDPDPERS TO TE SED mn OR. 
[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.] 
Supposed Horn-Sheaths of an Okapi. 
ARRIVING in London after an absence of more than 
three years in the Belgian Congo I have been con- 
siderably surprised at what appears to have been a 
mistake on the part of Messrs. Gerrard, the taxi- 
dermists, in connection with the skin and skeleton 
of an okapi, one of a series obtained recently by me 
in the Ituri forest. 
The okapi in question was sent to the director of 
the Tervueren Museum in Brussels, and afterwards 
forwarded by him to Messrs. Gerrard in London; 
the skin in one case, the skeleton in another. In 
the box containing the skeleton I had originally 
packed a number of other bones, including the skull 
of a very young waterbuck. These bones and the 
waterbuck skull were taken out in Brussels and 
retained for the museum according to agreement. 
Unfortunately, the detached horns of the young water- 
buck seem ‘to have been overlooked, and when found 
by Messrs. Gerrard it was assumed that they belonged 
to the okapi, with which, of course, they had nothing 
whatever to do. It would appear, moreover, from a 
letter in the columns of Nature of July 9, 1914 (vol. 
Xcili., p. 479), that the late Mr. Lydekker supported 
Messrs. Gerrard in this belief. 
If it is a fact that these two horn-sheaths were 
labelled as belonging to the okapi I can only say that 
this was not done by me or any of my servants in 
the Ituri, none of whom could speak or write any- 
thing but Kiswahili, and if any label had been 
attached in Brussels no doubt it would have been 
written in French. Nothing is mentioned in my 
register of specimens about horny-sheaths. On the 
contrary, I distinctly say, ‘‘Horns 1} in., skin- 
covered.” 
The extraordinary statement that the giraffe-like 
horns of an okapi, an animal far removed from the 
antelopes, could in any circumstances have horny- 
sheaths resembling those of the prongbuck, naturally 
aroused the interest of Sir E. Ray Lankester, whose 
knowledge of the anatomy of the okapiis unequalled. I 
am considerably indebted to him for going into the 
matter without waiting for my return, and dispelling 
the illusion. His view of what had probably hap- 
pened, as stated in his letter to Nature (March 18, 
1915), is perfectly correct, except as regards the 
‘well-intentioned servant.” 
The whole of my series of seven okapi skins has 
now safely reached England, I am glad to say, having 
been, through the kindness of the Belgian Minister, 
sent direct to London from the West Coast, together 
with two skeletons and various soft parts preserved in 
spirit. 
Altogether more than eighteen months were spent in 


