JUNE 24, 1915] 
NATURE 
465 

reality their bad shooting was due to pulling the trigger 
instead of pressing it. It is clear that more rapid 
progress can be made if the learner can discover the 
particular defect to which his failures are due. Various 
devices have been used for this purpose. 
In the sub-target the rifle is mounted on a universal 
joint, and on pressing the trigger a hole is punched in 
a card, thus indicating the direction in which the rifle 
is pointed at the instant. This appliance is expensive, 
and since the rifle is not free, defects due to trigger- 
pulling are not made evident. 
The aim-corrector is a piece of plain smoked glass 
mounted behind the rear-sight so that its surface is 
inclined at 45° to the sighting line. The learner takes 
his sight through this glass in the usual way; the 
instructor watches the sights from the side, as they are 
seen reflected in the glass. Obviously, the instructor 
must possess considerable skill in order to use this 
appliance with advantage. 
The aiming disc is a perforated metal disc which is 
placed in the observer’s eye like a monocle. The 
learner aims at the perforation, and any considerable 
motion of the rifle during trigger-pressing can be seen 
by the observer. This appliance can only be used with 
advantage at short distances from the learner, and 
anyone accustomed to the use of fire-arms can scarcely 
avoid an uncomfortable feeling on watching a gun that 
is pointed at his eye. 
I have devised a simple appliance by means of 
which most (if not all) of the benefits usually derived 

Fic. 5. 
from a miniature range can be obtained without the 
use of ammunition. This appliance is represented 
diagrammatically in Fig. 5. A metal tube T, which 
can be fitted to the bayonet standards of a rifle, is 
provided with a lens L at the front end, and a small 
electric glow-lamp G at the rear end. The lens L 
can slide in or out, so that the image of the glowing 
filament of the lamp can be focussed on a white screen 
placed near the target. The current for the lamp can 
be supplied by three or four Leclanché cells; or a 
battery of dry cells, similar to that used for an electric 
torch, can be fixed to the tube T, thus obviating the 
inconvenience of the leads from the lamp to the cells. 
It is best to aim at a target about 10 yards away; an 
observer, who need possess no qualifications other than 
general intelligence and quickness of perception, stands 
or sits by the target and watches the image of the 
filament formed on the screen. J have obtained small 
electric glow-lamps which produce an image approxi- 
mating in shape toa V. The position of the point of 
the V, at the instant when the trigger is pressed, can 
be marked on the screen; and if the rifle is moved 
during the act of trigger-pressing, the direction of 
motion, and its extent, can be marked by an arrow. 
If the position of the point of the V has previously 
been marked when the rifle was aimed by an expert, 
the correctness or otherwise of the learner’s sighting 
is seen at a glance. I have found that most learners 
aim better than they shoot; that is, they sight the rifle 
on the bull’s-eye with some approach to correctness, 
and then pull it away while they are actuating the 
NO. 2382, VOL. 95] 

trigger. If the learner is particularly bad at sighting, 
the rifle may be supported on a sand-bag or tripod 
stand, and sighting can be practised until a satisfac- 
tory ‘‘triangle of error” is obtained. 
I have found, by the aid of the appliance just 
described, that different people can aim a rifle with 
perfect consistency according to the rules given earlier 
in this article. Epwin EDsER, 

THE SOUTH-EASTERN. UNION OF 
SCIENTIFIC SOCIETIES. 
HE twentieth annual congress of the South- 
Eastern Union of Scientific Societies was held at 
Brighton on June 2-5, under the presidency of Dr. 
J. S. Haldane, F.R.S. The presidential address was 
entitled ‘‘The Place of Biology in Human Knowledge 
and Endeavour.” Dr. Haldane gave to his hearers a 
deeper insight into the inexhaustible fulness of reality 
| which science only partly explores, and puts us on 
our guard against the error of mistaking partial and 
abstract results for complete knowledge. He ex- 
plained the marvellous nicety of the natural regulation 
of the act of breathing, and of the means by which 
constancy in the composition of the blood was main- 
tained, and used these instances to prove the un- 
wisdom of declaring ourselves to belong to either of 
the opposing schools of ‘“‘mechanists”’ or ‘ vitalists.”’ 
In face of the evidences of ‘torganic determination ” 
which these instances gave, neither of these hypotheses 
could satisfy. In like manner, the partial character 
of even the highest conception of biology and of all 
science must be recognised, and recognising this, we 
should not be ready, merely because they are not 
susceptible of scientific treatment, to undervalue or 
ignore those higher elements of human experience 
which we designated moral and spiritual. 
Incidentally, in noble and moving language, Dr. 
Haldane referred to the great struggle which is 
occupying all minds. ‘The flashes of war have lit 
up for us this spiritual world. The sense that it is 
our plighted duty to deal with an infamous disregard 
of elementary right has sent hundreds of thousands of 
our best and truest into the fighting line, and is mar- 
shalling the whole activities of our nation and its 
Allies in a manner in which they never were mar- 
shalled before. . . . Yet we are waging this war in 
the absolute determination to conquer, cost what it 
may. For we are fighting, not merely for our own 
advantage or safety, but for a higher duty; and the 
faith that this higher duty is a real one, and that in 
following it we are at one with that spiritual reality 
which is the only reality, gives us a resolution, a 
courage, and a confidence, which could come from 
no other source.” 
In a paper on the problem of terrestrial and fluviatile 
shellfish, Mr. Hugh Findon dealt with the genealogical 
history of genera of molluscs, tracing their ancestry by 
the aid of the geological record, and finding the 
ancestral habit at one time marine, and at another a 
fresh-water one. ‘‘As I read the geological evidence 
the history of the river mussels is exceedingly interest- 
ing. A line of marine mussels persisting from earliest 
ages until the present time gave off a branch which 
in Carboniferous times took to a fresh-water life, 
Anthracosa, and again in the Miocene period repeated 
the phenomenon in Dreissensia. The first branch, 
with the exception of Anthracosa, returned to the sea 
and gave rise to another persistent family, that of 
Trigonia. About half-way along this second line a 
branch was given off which also entered a fresh-water 
existence during the age of the Purbeck, and this time 
successfully, for the present age witnesses Unios 
flourishing as they never did before in the world’s 
