| Sept. 8, 1870] 
NATURE 
379 
heavy rifled guns, in which an evenly burning product is 
an absolute necessity ; and indeed the most important 
condition to be fulfilled in gunnery science is always to 
employ ina gun that powder which is best adapted to the 
arm. Nowit is a well-known fact that the larger the 
grains of powder are made, the slower does a charge of 
it burn, supposing always the particles to be uniform in 
size, and not of a thin chip-like character, or irregular 
in shape. In rifled guns a slow, regular-burning powder 
is a sine gud non, for, unlike the case of smooth-bore 
howitzers and mortars, a steady and increasing push, 
and not a violent jerk, is necessary to force the projec- 
tile through the grooves. For mortars, therefore, a com- 
paratively fine-grain powder is employed, while for big 
rifled cannon a material of the coarsest description, with 
grains approaching in size that of a hazel nut, is invari- 
ably preferred. 
The best charge for a gun, especially if rifled, is more- 
over that which increases in power as the shot passes 
through the bore, and which exerts its greatest force.as the 
projectile leaves the muzzle, dv¢ not earlier; so that, on 
the one hand, the maximum explosive power is not 
put forth until the instant the mouth of the gun is 
reached and the last impetus given, while on the other 
hand no loss of power is suffered by the charge still 
burning after the bore is empty. If the charge burns 
quickly the shot is brought into action too rapidly, and 
the gun consequently subjected to excessive strain’; 
whereas, if the combustion of the powder is too slow, the 
shot does not receive the full benefit of the charge, and a 
large portion of it is lost. Thus, as may easily be 
imagined, the difficulty has hitherto been to fix upon the 
precise description of charge necessary tothe gun, and it 
is just this difficulty that has recently been solved by the 
elaboration of an instrument which accurately informs us of 
the velocity of any shot during its passage through the gun. 
The possibility of discovering what takes place in the 
bore of a cannon at the time of its discharge, and of 
ascertaining how fast the shot travels, is a subject that has 
long attracted the attention of artillerymen, and among 
others that ofa talented officer, Captain Andrew Noble, of 
the Elswick Ordnance Works. This gentleman’s labours 
have recently been crowned with success ; and an appa- 
ratus has been devised of which one hardly knows 
whether to admire more its exceeding delicacy or its 
wonderful results. With its aid the examination of gun- 
powder is now being conducted with comparative ease, 
and what is still more important, with unerring certainty. 
A detailed description of the instrument, which has 
received the name of Chronoscope, would necessitate 
more space than we have here at our disposal, but 
its main features, and the principle upon which it is 
based, are easily explained. The tube or bore of a gunis 
fitted inside at certain intervals with metal rings (to the 
number of six or eight) the outside margins of which are 
sharpened into so many knife-edges. Ona shot passing 
along the bore and through these rings, the edges of the 
latter are jammed down upon and made to cut through 
the ends of various insulated wires, one of which is 
placed under each ring. If we now suppose each of 
these wires to be in connection with an electric battery, it 
follows as a matter of course that as one wire after 
another is cut through, and the insulation consequently 
removed, an electric current passes ; so that if there are 
six rings and wires fitted at intervals in the tube of the gun, 
the passage of a shot along it would be instrumental in 
producing six electric sparks following rapidly one upon 
the other. 
We now understand how the shot is made to tell the 
tale of its flight ; but there remains yet to be explained 
how the story is written down. This recording of the 
signals is accomplished by a very simple arrangement. 
A series of metal discs, one in connection with each wire, 
is made, by means of a clock-work arrangement, to re- 
volve at a certain rapid velocity, say at the rate of 1,000 
inches in a second ; the surface of the discs is of polished 
silver, coated with lamp-black, and as soon as the 
desired speed has been attained, the gun, which is in 
electrical communication with the instrument, is fired. 
As the shot traverses the first ring, No. I wire is cut 
through, and a spark thereupon hops over to the record- 
ing disc, removing a little of the lamp-black covering, and 
thus marking the place by laying bare a minute spot of 
bright metal. No. 2 wire, when cut by the second ring, 
leaves a similar record upon another disc precisely in the 
same manner; and so on with Nos. 3, 4, 5, and 6, the re- 
lative position of the six spots on the six discs indicating 
exactly the velocity with which the shot has passed the 
six different rings or stations. 
A very simple calculation is now necessary to get at the 
results ; if there is a distance of one inch between each 
point, we know that one-thousandth part of a second has 
sufficed for the shot to travel from one ring to the other, 
for we remember that the discs were revolving at the rate 
of a thousand inches per second. This, however, only by 
way of example, for as a matter of fact we may mention 
that a shot usually takes from 515th to s};th of a second 
to traverse the whole length of the bore, its speed being 
somewhat slow when passing the first rings, and increas- 
ing as it approaches the muzzle of the gun. 
A certain amount of correction is of course necessary 
when reading off the results, but the accuracy of these 
may at any time be verified. Thus, in order to ascertain 
whether the electric and mechanical arrangements of the 
discs are in good order, it would be necessary merely to 
place the whole number of wires together under a single 
ring, so as to be cut through at one and the same 
moment, when the points on the discs should, of course, 
all coincide. 
The great importance of this beautiful invention need 
not be dilated upon by us, as the value of its aid in expe- 
riment is at once apparent to the veriest tyro in gunnery. 
As a measurer of time and speed of the most perfect 
character, its delicacy is certainly unsurpassed ; for, by 
merely dividing every inch of the discs into a thousand 
divisions or degrees, we are at once enabled to calculate 
with precision to the millionth part of a second. 
NOTES 
A WEEK or two ago we announced a rumour to the effect that 
the Government had refused to allow a ship to convey the 
eclipse observers to Spain and. Sicily next December. The 
rumour was too well founded; the Government has actually 
refused to tell off a ship for this purpose. This decision in 
the teeth of the plainest precedents requires no comment 
on our part; in fact, it is beyond all comment, it is 
astounding. We are enabled to announce, however, that the 
American Government, more enlightened than our own, are 
making extensive preparations ; and upon theresults of their labours 
and those of the Continental Governments Englishmen must there- 
fore fall back, ina research which is eminently English. The 
Americans will send three corps of observation, to be stationed 
respectively at Malaga, Sicily, and some place in Turkey most 
available for making the best scientific records and views. One 
of these corps will be sent from the Naval Observatory, and the 
other two will be composed of the most scientific men in the 
country, including the professors from Harvard University. 
Before the war broke out it was arranged that Rear-Admiral 
Glisson should extend to the corps at Sicily all the aid and co- 
operation in his power. But the original plan has been spoiled 
for the present by the troubles in Europe, Admiral Glisson being 
obliged to move his squadron to the Baltic for the protection of 
American commerce in that vicinity. 
WE regret to learn that the health of Gen. Sir E. Sabine, the 
distinguished and yenerable president of the Royal Society, is at 
