460 
NATURE 
[Marcu 18, 1897 
American and Colonial, which are again sub-divided 
into alphabetical and classified sections ; in the case of 
the British, a Geographical Section has been added, 
making in all nine sub-divisions. 
Photography as a Hobby, “The Popular Photographic 
Series.” By Matthew Surface. Pp. 60. (London: Percy 
Lund, Humphries, and Co., Ltd., 1897.) 
THIS little book is intended for those who amuse them- 
selves with photography. The author shows how many a 
pleasant hour may be spent with the camera, and describes 
rambles he himself has made. These are very well 
illustrated, and the reader will gather from them that it 
is not necessary to go very far afield for subjects, as 
these are always close at hand if one only has the 
capacity for picking them out. The author describes 
also how, during unfavourable weather, the “hobby” 
may be carried on in the house. The book is very neatly 
got up, and will afford those who indulge in photography 
as a hobby with a pleasant hour’s reading. 
First Records of British Flowering Plants. 
by William A. Clarke, F.L.S. Pp. 103. 
West, Newman, and Co., 1897.) 
TO satisfy commendable curiosity, it is often required to 
know who first observed a particular plant, when and 
where it was first found,and how long it has been known 
as a British plant. The answers to these questions will be 
found in Mr. Clarke’s handy little volume. The earliest 
notice of each distinct species of British flowering plants 
has been found by searching through printed botanical 
works published in Great Britain, and the extracts thus 
obtained have been brought together in this work. The 
list contains altogether 1440 species, the nomenclature of 
which is based upon the eighth edition of the “ London 
Catalogue.” The earliest records referred to are from 
William Turner’s works, ranging from 1538 to 1568. 
Compiled 
(London : 
On Human Nature. By Arthur Schopenhauer. Translated 
by T. Bailey Saunders, M.A. Pp. 132. (London: 
Swan Sonnenschein and Co., Ltd., 1897.) 
HUMAN nature as understood by that most pessimistic of 
philosophers, Schopenhauer, is here presented in English 
dress by Mr. Saunders. The essays which make up the 
book have been selected and translated from Schopen- 
hauer’s Paverga. They deal with human nature in 
various aspects, and their tendency is to make a man 
suspicious of all people, distrustful of all motives, and 
doubtful whether civilised life is real or only a big 
masquerade. 
Tabellen fiir Gasanalysen, gasvolumetrische Analysen, 
Stickstofibestimmungen, &c. By Prof. Dr. G. Lunge. 
(Braunschweig: Friedrich Vieweg und Sohn, 1897.) 
THESE tables will be found of service in chemical 
laboratories in which gas analyses, and volumetric deter- 
mination of gases, are made. One of the tables is for 
the reduction of the observed volume of a gas to the 
temperature of o°, and the other enables the observed 
volume to be reduced toa pressure of 760 mm. Together 
the tables thus furnish the means for reducing volumes 
of gases to standard temperature and pressure. 
The Larve of the British Butterflies and Moths. By 
the late William Buckler. Vol. vii. Edited by Geo. 
T. Porritt, F.L.S. Pp. 176. 22 plates. (London: 
Ray Society, 1897.) 
THE first volume on the larvee of the British butterflies 
and moths appeared in 1885 ; the present volume con- 
tains, the first portion of the Geometre, and this group 
will be completed in vol. viii. The twenty plates illus- 
trating the larvae described are extremely fine, and the 
whole volume is a worthy addition to an invaluable 
series. 
NO. 1429, VOL. 55 | 
LETTERS TO THE EDITOR. 
[Zhe Editor does not hold himself responsible for opinions ex- 
pressed 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 ts taken of anonymous communications. | 
The Measurement of Pressures in the Bore of Guns- 
It has been stated that many gunpowders which have given 
fairly satisfactory results in a small bore, have developed 
dangerous pressure when tried in cannon; and also that 
similar experiments with cordite showed no signs of any 
approach to such a ‘‘critical point.” Further, cordite is said 
to burn quietly when thrown in boxes of 100 lbs. upon a bonfire, 
and yet to be as suitable for ordnance as for small arms. But 
cordite did not prove so tractable on its late trial in Plumstead 
Marshes. It is plain, therefore, that explosive forces of all 
powders depend very much upon the conditions under which 
they are ignited. 
Hence arises a pressing necessity for some satisfactory method 
of determining the maximum explosive force which every 
adopted powder is capable of exerting when fired in xzfed guns 
of small and large calibre. The chronoscopic method of solving 
the problem was brought forward thirty years ago, under the 
then Ordnance Select Committee, but I have never met with a 
single example fairly worked out for a 7z/led gun, so as to show 
precisely what could be found by that method. My difficulty 
was stated in NATURE (March 14, 1895), but hitherto without 
result, except that the President of the British Association, in 
his address at Ipswich (September 1895), stated that— 
*©In the gun, by means of electrical contacts arranged in the 
bore, a ¢2e-curve of the passage of the shot can be determined. 
From this the mathematician constructs the velocity-curve, and 
from this, again, the Aresswres producing the velacity are es/z- 
mated (?) and used to check the same zndzcatéons obtained by 
other means (p. 29).” ~ 
Now, beside the ‘‘ pressures producing the velocity” of the 
shot in 72fed guns, there is an additional force arising from 
friction, &c., which greatly adds to the pressure of the powder 
gas tending to burst the gun. Hence, if we denote by P this. 
pressure of the powder gas on the base of the shot, and by F 
the retarding pressure of friction, &c., at the same instant, then - 
the resultant driving pressure acting on the shot will be denoted 
by (P—‘F) at that instant. If now the projectile be made to 
trace an accwate time-curve, it will be possible to deduce from 
this time-curve the value of the driving pressure (P—F) acting 
on the shot at every point. But the grand object is to find P, 
the pressure of the powder gas tending to burst the gun, and 
not (P—F) the pressure driving the shot, which is given by the 
chronoscope. Therefore the chronoscopic method of experi- 
menting fails to give the whole pressure of the powder gas, which 
tends to burst the 7zfed gun ; and this method gives nothing 
which can be ‘‘ used to check the same indications obtained by 
other means,” simply because (P—F) is not given by other 
means. The chronoscopic method of experimenting fails when 
any part of the pressure (F) of the powder gas is not instrumental 
in producing motion. From what has been said, the chrono- 
scopic method must fail, even under the most favourable circum- 
stances, when vzfled guns are used. 
But the perfect accuracy in experiment we have assumed can- _ 
not be secured practically. The most critical point is at the 
instant the shot begins to move. But no chronoscope which 
registers by fozzts can make the smallest pretence to give the 
initial time-curve accurately. 
The only way to find the pressure of the powder gas at any 
point in the bore of a 7zffed gun is to use a modification of 
Rumford’s or Rodman’s method, which measures directly the 
pressure in the bore at any point. 
The vast importance of this subject to the nation at this time 
must be my excuse for troubling you a second time. 
Minting Vicarage, March 4. F, BASHFORTH. 
A Powerful and Efficient Means of Driving X-Ray 
Tubes. 
DuRING the last few months the limitations of the present 
induction coil, especially as a means of driving X-ray tubes and 
vacuum tubes in general, have been so clearly brought before 
us that we have given the subject considerable attention. It is 
