478 
(4) This is one of Mr. Maycock’s many works 
on electrical subjects, and is intended to deal with 
the requirements of Grade I. and the final exam- 
inations in electric wiremen’s work of the City 
and Guilds of London Institute. It is therefore 
essentially a book for beginners, and as such can 
be recommended. It contains a number of ques- 
tions and their solutions. 
OUR BOOKSHELF. 
Careers for Our Sons. A Practical Handbook to 
the Professions and Commercial Life. Edited 
by the Rev. G. H. Williams. Pp, xii+ 564. 
Fourth edition. (London: A. and C. Black, 
1914.) Price 5s. net. 
Tuat this book has reached a fourth edition since 
its first appearance ten years ago is an indication 
of its usefulness to parents and guardians. There 
are few more baffling tasks than to find a suit- 
able opening for a boy whose school and college 
training are completed, but who has no clear idea 
of what he desires to do to secure a livelihood. 
To those who are face to face with the problem 
this complete and well-arranged compilation may 
be recommended confidently. Mr. Williams is an 
old schoolmaster who has supplemented his own 
wide experience by much valuable information 
gathered from «a large number of experts. 
By P. M. C. Kermode and 
Second edition. Pp. 
Press,’ 1614.) 
Manks Antiquities. 
Prof. W. A. Herdman. 
150. (Liverpool: University 
Price 35. (net: 
TuE first edition of this book, which was out of 
print for some time, was reviewed at length in 
the issue of NarureE for June 14, 1906 (vol. Ixxiv., 
p- 152). During the ten years since the original 
appearance of the work, the authors have ex- 
plored several additional prehistoric sites, and a 
systematic survey of the antiquities of each parish 
has been undertaken by a committee of the Isle 
of Man Natural History and Antiquarian Society. 
From these and other sources much new material 
has been worked into the present edition of the 
book, which will prove of interest and service to 
the people of the island and their summer visitors. 
Royal Society of London. 
Papers, 1800-1900. Subject Index. Vol. iii., 
Physics. Part II., Electricity and Magnetism. 
Pp. xv+927+Vvii. (Cambridge: The University 
Press, 1914.) Price 15s. net. 
Catalogue of Scientific 
In the review of the first part of the third volume 
of the Royal Society’s catalogue of scientific 
papers, which appeared in Nature on May 22, 
1913 (vol. xci., p. 289), the general plan and scope 
of the work were described. It will be sufficient 
to say of this part that it completes the subject 
index on physics, deals with electricity and mag- 
netism under the registration numbers 4900 to 
6850, and contains 23,300 entries. This makes 
in all 56,644 entries for the subject physics for 
the years 1800-1900 inclusive. 
NO. 2232) VOl. 5o3)) 
“A143 
NATURE 
ESS 
es 
[JuLty 9, 1914 
LETTERS TO) JE” EIR. 
[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. | 
Active Nitrogen. 
In view of the apparently inexplicable contradiction 
between the results of Tiede and Domcke (Ber., 1913, 
46, 340 and 4095) and Baker and Strutt (Ber., 1914, 
47, 801 and 1049) on this subject, Tiede and Domcke 
offered to visit London with their apparatus, and it 
was arranged that each pair of experimenters should 
repeat their experiments in presence of the other. 
This was done, and as a result it was agreed that 
Tiede and Domcke were justified in their statement 
that the addition of a trace of oxygen to the azide 
nitrogen increased the intensity of the glow. With 
the form of discharge vessel and the electrical equip- 
ment used by them it was possible to diminish the 
afterglow considerably, and then to restore the bril- 
liancy of the glow by the addition of an infinitesimal 
trace of oxygen, liberated by gentle heat from silver 
oxide. When the amount of oxygen added exceeded 
this very small quantity, the glow entirely disappeared, 
as all former experimenters have agreed. 
On the other hand, employing the form of discharge 
vessel used by Baker and Strutt, which has not been 
described in detail, but is better designed for obtaining 
the glow, it was not found possible to observe any 
distinct diminution in the intensity of the glow, even 
when the vessel was washed out several times with 
nitrogen prepared by Tiede and Domcke with their 
own materials, as used in the previous experiment. 
It is always possible that if the experiment had been 
more prolonged a different result might have been 
obtained. 
It appears, therefore, that a sample of nitrogen may 
be made to give the glow moré easily if it is mixed 
with a trace of oxygen. On the other hand, the 
purest nitrogen with which we have worked in our 
joint experiments in London is capable of giving a 
brilliant glow under the experimental conditions used 
by Baker and Strutt. 
It seems possible that the effect of the infinitesimal 
trace of oxygen is to alter the conditions of discharge 
so as to make it more suitable for the production of 
active nitrogen. Prof. Warburg’s observations of the 
effect of traces of oxygen on the kathode fall in 
nitrogen tends to confirm this idea. Possibly other 
substances than oxygen may be found eventually to 
produce the same effect. 
H..B. Baksrr. 
EricH TIEDE. 
R-~ J. “STRODE: 
Emit Domcke. 
Imperial College of Science and Technology, 
London, July 2. 
The Horns of the Okani. 
HirHERTO it has been considered that the horns of 
the male okapi, with the exception of the bare antler- 
like terminal caps, are permanently covered with hairy 
skin, like those of giraffes. The skin and skeleton 
of an old male okapi recently sent to Messrs. Gerrard, 
of Camden Town, by Dr. Christy, seem, however, to 
indicate that, extraordinary as it may appear, true 
horn-sheaths, like those of antelopes, are developed in 
at least some individuals. The skull, which, from 
the condition of the teeth, indicates an animal at least 
