506 
NATURE 
[JuLy 8, 1915 

gases in war and the massacre of women and 
children. We would rather suggest that musical 
art possesses an element of permanence which is 
not to be found in the other arts. The collection 
of masterpieces which the present generation has 
inherited from the classical composers is so large 
that a modern composer, working on the same 
lines, would find it next to impossible to assert 
his influence. Consequently, musicians have had 
to seek fresh fields and pastures new by tearing 
up the ‘‘scraps of paper’ which their predecessors 
regarded as binding. 
“c 

OUR BOOKSHELF. 
Surface Tension and Surface Energy and Their 
Influence on Chemical Phenomena. By Dr. 
R. S. Willows and E. Hatschek. Pp. vili+8o. 
(London: J. and A. Churchill, 1915.) Price 
2s. 6d. net. 
THE appearance of this book, following close on 
that of a similar work by Michaelis, is a welcome 
sign of. the increasing interest now taken in this 
subject. The distribution of matter and energy 
at any interface, although of the first importance, 
has only come into prominence since the develop- 
ment of colloid chemistry. 
The scope and character of the book may be 
indicated by a reference to the chief subjects 
discussed. They are:—the fundamental ideas of 
surface tension ; intrinsic pressure; Gibbs’s surface 
excess formula; recent experimental work on 
interfacial concentrations ; electrical phenomena at 
interfaces, with special attention to the Lippmann 
electrometer and the dropping electrode; and, in 
conclusion, such matters as condensation on gas 
ions, effect of electrification on the vapour 
pressure of drops, and ‘waterfall electricity.” 
It_is scarcely surprising. that the authors have 
found it no easy task to co-ordinate these varied 
subjects; and to this difficulty is doubtless due a 
want of clearness in a few places. There is one 
notable omission; one would have expected to 
find the development of the surface excess equa- 
tion, either as given by Gibbs himself, or 
by Thomson or Milner. Curiously, no mention is 
made of Milner’s experimental work, the first 
attempt to test the formula. 
In spite of these defects, the work must prove 
helpful to advanced students and_ research 
workers, biological and technical, who have a 
practical interest in adsorption and allied 
phenomena. There is a useful index, but it 
seems a pity that no references to original papers 
are given. Viva Wwe Be 
Fire Tests with Glass. ‘‘Red Books,” Nos. 196 
and 197. (London: British Fire Prevention 
Committee.) Price 2s. 6d. each. 
THESE two small books embody the British Fire 
Prevention Committee’s Report on Fire Tests 
made respectively with skylight openings and 
windows filled in with “wired glass” manu- 
NO. 2384, VOL. as! 



factured in our own country. The skylights were 
five in number, each 2 ft. square, and arranged 
horizontally in a single straight row. The glazing 
was subjected to fire for an hour, followed by 
water from a steam fire-engine applied at close 
range for two minutes on the fire side. No fire 
passed through the glazing, but more or less water 
found its way through three of the five. Details 
of the tests are given, with illustrations showing 
the effects of the fire. The three vertical windows 
were subjected to a precisely similar test with 
much the same results. In the case of two of 
the windows neither fire nor water passed through 
the glazing, but in the third, though no fire 
passed through, the application of water caused 
perforation and some water got through. The 
temperatures reached before ‘the application of 
water were not less than 1500° F. (or 815°5° C.). 
The maximum size of the vertical glazing tested 
was four feet by one foot. 
The results of the tests clearly indicate that 
British wired glazing, when suitably fixed, can 
effectually check the spread of fire in a manner 
comparable with fire-resisting partitions and 
doors of much greater thickness and weight. The 
subject is well worth the serious attention of 
those interested in the limitation of damage by 
fire, especially in cases where the admission of 
light is desirable. J. A A 
LETTERS 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. | 

The Okapi. 
In my letter published in Nature of May 27 (vol. 
xcv., p- 342) dealing mainly with the ‘Supposed 
Horn-Sheaths of an Okapi,’’ I stated that ‘‘it is only 
when extremely young that the backward slope of the 
back is very noticeable.’”’ It is perhaps the only state- 
ment I have made regarding the okapi which was not 
based on my own observations, and it appears to be 
erroneous. The impression was derived from a photo- 
graph reproduced in M. Fraipont’s ‘“‘ Monograph on 
the Okapi,” of a very young one captured by natives 
and brought into one of the Uele stations. I have 
since seen a photograph of the same animal from 
another source which shows that there was very little 
backward slope. At maturity the height of the okapi 
at the shoulders is only 2 to 3 in. at the most more 
than that above the hindquarters. The following 
measurements taken from three animals lying as they 
fell, one by Mr. A. E. H. Reid, and two by myself, 
bring this out quite clearly :— 
Young Old Old male 
male female (Reid's) 
(No. 507) (No. 686) (No. 717) 
ft. in. ft. in. fr. 
Nose to tip of tail Keeton hate elOd Tin Ome icone g a 
Tatli(withontshair)).... ... <.. sa, euray 014 14 
Height at shoulder Mees 6. MS ose i 4 
Height above hind quarters .. 

o =, 0 
Cm e eed thes 
ee 2d al Te 
fo} Oo 
Excess of height at the shoulders... 


