ee 
Dec. 29, 1870 | 
NATURE 
169 

glycerine, known as dynamite, and which is simply pow- 
dered glass or sand saturated with the explosive, was 
applied in the experiments ; the force of the dynamite 
very nearly equals that of nitro-glycerine, and is of course 
much more readily handled than the liquid explosive itself. 
Nitro-glycerine or its compounds are the only agents of 
this nature that can compete in any way with gun-cotton, 
either as regards its igniting force or cost of production ; 
and for this reason the experiments with these two 
materials have been watched with particular interest by 
military men, and have indeed formed the subject of a 
special report recently submitted to Government by the 
Committee on Explosives. 
The explosive force of detonated dynamite and the 
Abel gun-cotton, as the compressed or pulped form of 
this materialis termed, was considered to be about equal, 
and on this account the investigation was more particularly 
confined to the methods of ignition of the two substances. 
Professor Abel had already shown, in his communication 
to the Royal Society, that gun-cotton detonated only 
under certain conditions and but by the instrumentality 
of particular agents. And here it should be borne in 
mind that there exists a very great difference between 
the detonation and inflammation of gun-cotton. A block 
of the compressed material, for instance, may be set fire to 
in an ordinary room without the semblance of danger, 
the cotton burning vigorously and rapidly, it is true, but 
without any approach to explosion ; ignited, however, by 
means of a small quantity of fulminate of mercury or 
fulminate of silver, the explosion is of the most violent 
description. The fulminates above-named are the only 
ones found to bring about the ignition of gun-cotton in 
this truly terrible manner ; iodide of nitrogen fails to have 
any effect thereon, and chloride of nitrogen is occasionally 
successful in doing so, provided it is employed as a primer 
in sufficient quantity. While, however, gun-cotton is thus 
very difficult of detonation, except by the use of special 
means, nitro-glycerine, or dynamite, readily detonates 
under ordinary circumstances. ‘That is to say, not only 
do the fulminates above-mentioned secure its ignition, 
but percussion-cap and other compositions, as a'so a sharp 
concussion, inevitably bring about its combustion, 
An interesting experiment will indeed show at once the 
marked difference between the two explosives. Two 
wooden boxes were filled with compressed gun-cotton and 
dynamite respectively, and placed in a suitable position at 
a rifle range, where they could be hit with certainty by 
small arms. A bullet was fired at each box, and the re- 
sults were very conclusive ; the dynamite detonated in a 
terrible manner at the shock, while the gun-cotton was 
merely inflamed, and burned in arapid but steady manner. 
It was further found that in order to secure certain and 
perfect detonation, it was always necessary to employ a 
much larger and more powerful detonating fuze (one con- 
taining a large amount of fulminate) for the explosion of 
gun-cotton than was required for nitro-glycerine, proving 
beyond doubt, therefore, that the latter is much more 
readily ignited than the fibrous material. This is of 
course a great safeguard, and added to the fact that under 
many circumstances of accidental ignition gun-cotton 
inflames harmlessly and does not detonate, speaks much 
in favour of pyroxiline. Indeed the use of nitro-glycerine 
can, according to our best authorities, be applied only 
within very narrow limits, as, for instance, for blasting 
and mining purposes, and its employment even in this 
sphere necessitates very careful supervision. 
From this it will be at once seen that the recent prog- 
nostications of several of our war correspondents that the 
Prussians intend to employ dynamite shells in the bom- 
bardment of Paris must be entirely without foundation, for, 
according to the results obtained by the Explosive Com- 
mittee in this country, the discharge of a nitro-glycerine 
shell from a gun would be of itself sufficient to bring about 
the immediate bursting of the arm itself. 


ASSOCIATION FOR THE REFORM OF GEO- 
METRICAL TEACHING 
HE following circular has just been issued :—“ For 
sometime past an effort has becn made to im rove the 
teaching of Geometry in English schools, The undersigned 
--all mathematical teachers--are of opinion that good would 
result from the formation ofan Association for the Reform 
of Geometrical Teaching, and are desirous to elicit the 
opinion of others who may be interested in the movement, 
The objects of such an Association would be—r. To col- 
lect and distribute information as to the prevailing methods 
of instruction in geometry practised in this and other 
countries, and to ascertain whether the desire for change 
is general. 2. To use its influence to induce examining 
bodies to frame their questions in geometry without refer- 
ence to any particular text-book, 3. To stamp with its 
approval some text-book already published, or to bring 
out a new one under its own auspices. Should you be 
willing to become a member of such an Association, you 
are requested to send your name and address, with a small 
subscription to meet the necessary expenses of printing 
advertising, &c., to Mr, Levett, King Edward’s School, 
Birmingham. (Signed) Rawdon Levett, M.A., Senior 
Mathematical Master, King Edward’s School, Birming- 
ham ; E. F. M. MacCarthy, M.A., Second Master, pre- 
siding over the Modern Department, King Edward’s 
School, Birmingham ; J. M. Wilson, M.A., late Fellow of 
St. John’s, Cambridge, Mathematical Master of Rugby 
School; Robert Tucker, M.A., late Scholar of St. John’s 
College, Cambridge, Hon. Sec. London Mathematical 
Society, and Mathematical Master, University College 
School.” 
A Conference is intended to be held on the 17th of 
January, 1871, at 2.30 P.M., in the Mathematical Theatre, 
University College, London, Dr. Hirst in the chair, for the 
following purposes :—The Association will first be or- 
ganised, The following resolutions will then be pro- 
posed: 1. “That the main object of this Association is 
to induce all conductors of examinations, at which pupils 
who have been trained under different systems present 
themselves, to frame their questions independently of any 
particular text-book ; and that with a view to this object, 
the members present at this meeting do pledge themselves 
to use every effort to increase the numbers and extend 
the influence of the Association.” 2. “ That with a further 
view of extending the influence of the Association, local 
secretaries be appointed for different parts of the kingdom, 
whose office it shall be to collect information, to make the 
objects of the Association more generally known in their 
immediate neighbourhood, and to communicate on all 
matters of interest with the Central Committee.” 3. “ That 
the local secretaries, zfso facto, be members of the com- 
mittee of management.” 4. “That all members of the 
Association shall collect information with regard to text- 
books and methods of teaching geometry in England and 
other countries, and that such information shall be for- 
warded to any secretary or local secretary of the associa- 
tion.” 5. “That the committee of management shall, 
from time to time, print and circulate among others such 
information as they may consider valuable.’ 6. “ That 
this meeting is of opinion that in any new text-book—(a) 
the following principles, only partially or not at all recog- 
nised by Euclid, should be adopted :—(i) hypothetical 
constructions, (ii) the arithmetical definition of proportion, 
(iii) superposition, (iv) the conception of a moving point, 
and of a revolving line; (4) the following limitations 
should be removed :—(1) The restriction of the number of 
axioms to those only which admit of no proof, (ii) The 
restriction which excludes all angles not less than two 
right angles ; (c) modern terms, such as locus, projection 
&c., should be introduced. These points will be voted 
upon in detail, 
