434 
of after-image, the drift set up by moving objects in 
the organs of vision—these things have been. illus- 
trated as isolated optical illusions and not brought 
together as a systematised whole. In this respect the 
programme of the Optical Convention somewhat 
strikingly reproduces the state of scientific knowledge 
at the present time. There is a very large amount 
of information as to the phenomena which are ex- 
ploited for the representation of movement, but very 
little of systematic thought or systematised writing on 
the subject. It will be perhaps not the least useful 
result of the Optical Convention if its shortcomings 
in this respect should direct the attention of the 
scientific world to the unformed condition in which 
at the present moment the theory of the imagery 
of motion exists. 
Passing from the question of novelty and coming 
to that part of the work of the convention which is 
concerned with taking stock of the state of know- 
ledge, we note that the papers submitted have 
covered, as was to be expected, a very wide range, 
and have been characterised upon the whole by a 
high degree of utilitarian value. The executive com- 
mittee of this convention has been able to secure 
the very active cooperation in connection with this 
branch of their work of the leading scientific societies 
which are definitely concerned with the study of 
optics. Thus by means of joint meetings of the mem- 
bers of the convention with the members of the Royal 
Astronomical Society, the Royal Photographic 
Society, the Physical Society, and the Optical Society, 
a very high level of interest in this part of the work 
of the convention has been maintained. The direct 
participation of these societies has secured large 
attendances at the meetings of the convention, and 
these again have reacted helpfully in the way of 
promoting the success of the exhibition. 
The active cooperation of these societies with one 
another and with the promoters of the convention 
in relation to objects in which they have a common 
interest may be from every point of view regarded 
as an innovation of happy augury. It is impossible 
at the present day for scientific knowledge to be 
grappled with as a whole. Students and _ societies 
must specialise ; and a very high degree of specialisation 
is essential to the successful carrying on of every 
department of scientific work. But specialisation has 
its perils as well as its advantages, and a mischief 
which, in fact, results from over-specialisation is 
that the spread of knowledge may to a certain extent 
be hindered. One investigator here, wrapped up in 
his own subject and too exclusively monopolised by 
it, has, by reason of his preoccupation, less opportunity 
than he would otherwise possess of becoming 
acquainted with the results which another worker, 
isolated by his own specialisation, has reached else- 
where. This segregation of researchers and research 
is apt actually to be promoted by their division into 
separate societies, and it is an eminently helpful 
thing that they should find opportunities, such as this 
Optical Convention has afforded, of meeting together 
upon common ground to carry on the commerce of 
ideas upon a larger scale than their organisation for 
the purpose of special research permits. 
ably a good deal easier nowadays to start a new 
society than to establish conditions of cooperation 
among existing societies, even among those which are 
naturally affiliated by the objects of their pursuits. 
It is matter for congratulation that the four societies 
named have been able to cooperate, and to so good 
purpose, in connection with the meeting of the 
Optical Convention. 
The cooperation of these societies leads naturally 
to the mention of what seems likely to be the most 
No. 2226, vot. 89] 
It is prob- | 
NATURE 
[JuNnE 27, 1912 
permanent and perhaps the most valuable outcome of 
the Optical Convention of this year. Its promoters 
have succeeded in securing the formation of a very 
strong committee for the purpose of considering ques- 
tions touching the improvement of optical instruments. 
Such at any rate was the scheme with which the 
committee was originally formed, and in pursuit of 
that aim a widely extended inquiry has been set on 
foot for obtaining a statement by the users of 
optical instruments as to points upon which they 
consider that improvement is required. We under- 
stand, however, that, moulded by circumstances, the 
proceedings of this committee seem likely to take a 
somewhat larger scope. 
The announcement has been made that some impor- 
tant problems have been submitted as the result of 
the inquiry already referred to for the consideration 
of the committee, and that some of those problems 
touch not only upon the design of instruments but 
also upon the still larger questions of optical constants 
and nomenclature. It need scarcely be said that very 
important questions of this mature lie open for dis- 
cussion, and we can well believe that the committee, 
if it is to arrive at any practical result at all, will 
have to exercise a selection among the problems taken 
into consideration. As no definite statement has yet 
been made concerning the exact nature of the problems 
with which the committee will propose to deal, it is 
impossible to form any opinion at the present time 
as to the probable outcome of its labours. The scien- 
tific world, however, has learned with considerable 
interest that such a committee, consisting of Prof. 
S. P. Thompson, the Astronomer Royal, Sir William 
Abney, Sir David Gill, Dr. Glazebrook, Prof. Schuster, 
and Mr. Plimmer, has been formed for the purpose 
of dealing with such problems, and the results of 
their deliberations will be looked for with still greater 
interest. 
Another result of the meeting of the convention 
which will have an abiding value is the catalogue 
produced. This contains the most adequate repre- 
sentation it is possible to produce at the present time 
of the state of the British optical industry. The cata- 
logue has been compiled upon the same plan as that 
of 1905, but it is a considerably larger volume, extend- 
ing to nearly 400 pages. The introductory matter, 
which has been compiled with great skill, contains 
probably the best available statement of what has 
been accomplished in recent years by the designers 
and manufacturers of optical instruments in this 
country. The exhibitors’ account of their instruments 
will be found to be in many instances valuable specifi- 
cations of the optical appliances described, and in 
some instances we observe that the value of these 
technical descriptions is enhanced by reference to the 
bibliography of the instruments in question. Whether, 
therefore, the catalogue be considered from the indus- 
trial or from the scientific point of view, it must be 
pronounced an important work, and its production 
| should alone repay the optical industry in this country 
for the expense and trouble involved in bringing to- 
gether the materials for the exhibition. 
Of the third permanent result of the convention— 
the volume of Proceedings—it is as yet too soon to 
speak. A reference has above been made to the 
general character of the papers submitted, which will 
be reproduced in that volume, and concerning the dis- 
cussion to which those papers have been subjected it 
may be said that, although the limitation of time has 
militated against the success of those discussions, yet 
in many instances the discussions have been successful 
in spite of somewhat hard conditions, and may be 
expected to add materially to the value of the Proceed- 
ings when published. 
