et 
JUNE 27, 1912] 
NATURE 
4a 
This question of the pressure of time upon the dis- 
cussions is one of growing importance in connection 
with scientific congresses. On one hand it is essential 
to the success of such meetings that the programme 
should be open to a large number of papers, since 
otherwise it would not be possible to secure that 
extended view and free interchange of opinions and 
ideas which it is the object of such assemblies to pro- 
mote. But, on the other hand, if there are many 
papers to be discussed, the difficulty of discussing 
them within the available limits of time becomes ex- 
treme. We observe with interest that an attempt has 
been made in connection with this convention to cir- 
cumvent the difficulty by means of demonstration 
rooms. Two rooms were set apart in the buildings 
placed at the disposal of the committee for this pur- 
pose. 
stration Room—the diagrams and apparatus illustrat- 
ing papers were set up and maintained on exhibition 
during the whole period of the convention. It was 
thus possible for the members to study any particular 
paper at leisure, while the readers of the papers had 
the satisfaction of repeating their demonstrations to 
selected audiences. 
The other demonstration room, which was open to 
the public, served sometimes for the fuller discussion 
of a paper which had been inadequately discussed in 
the meeting room, and at other times for the accom- 
modation of impromptu demonstrations unconnected 
with the printed programme of proceedings. These 
seem both to have been useful expedients for minimis- 
ing the inconvenience of deficient time for reading and 
discussion of papers at the set meetings, and 
probably would have been more effective for 
the purpose if the arrangement had been more 
commonly adopted, and therefore better understood. 
But the best demonstration room expedient is but a 
palliative, and the problem still remains to confront 
the organisers of scientific and other congresses how 
to get the work before them accomplished in the time 
at their disposal. 
EXHIBITION OF OPTICAL AND 
GENERAL SCIENTIFIC INSTRUMENTS. 
‘Te success achieved by the Optical Convention 
of 1905 was a guarantee of that of the second 
account is given in 
connection with the 
an 
In 
convention, of which 
the preceding article. 
convention an exhibition has been held which 
has been representative of every branch of 
applied optics. The committee of the conven- 
tion has been deeply indebted to the Board 
of Education for the space in the South Kensington 
Museum galleries which has been placed at its dis- 
posal, and for the many facilities afforded, which have 
very greatly helped the success of the exhibition. 
The exhibits have been divided into twenty classes 
corresponding to as many types of optical apparatus, 
and a very interesting loan collection was organised, 
consisting of apparatus of historical interest and 
special apparatus of which in many cases only one 
has been made. Arrangements were made so that in 
many cases visitors could have the advantage of 
demonstrations by the gentlemen who had designed 
and used such apparatus in their researches. 
Among the most interesting of these were a set of 
gratings and similar apparatus belonging to the Royal 
Society, which were used by Fraunhofer in his re- 
searches on the spectroscope. A camera lucida belong- 
ing to the inventor, Dr. Wollaston, was lent by the 
master and fellows of Gonville and Caius College, 
Cambridge. Mr. T. H. Court lent a number of early 
NO. 2226, vo. 89] 
In one of them—called the Members’ Demon- | 
| effects. 
| microscopes, and Mr. Croft a number of very interest- 
ing photographs of interference and_ polarisation 
The hon. secretary, Mr. j. W. Gordon, pro- 
vided examples of many of the useful facilities which 
he has invented for microscopic workers. Messrs. 
Rheinberg gave demonstrations of the beautiful micro- 
spectroscopic method of colour photography, and 
Prof. Coker of the very different but equally beautiful 
method of studying the stresses in celluloid models of 
| engineering structures by the use of polarised light. 
| A very interesting small dividing engine for the pro- 
duction of diffraction gratings was shown by Mr. 
Pochin. In this a cast-iron screw has been adopted 
| as being far superior to mild steel, which was found 
to be comparatively useless. 
The Secretary of State for War has shown his 
interest in the exhibition by permitting an exhibit 
arranged by Major Williams of certain representative 
types of optical apparatus as used in the Army. 
A number of thermostats, silica mercury-vapour 
lamp, and silica vessels for use in polarimetry were 
shown by Dr. T. Martin Lowry. The latter are 
especially useful for liquids which are liable to be 
altered by the alkali contained in ordinary glass. 
The new gas and liquid refractometer of Messrs. 
Zeiss is an instrument of great sensitivity, being able 
| to detect one part in 100,000 of salt in its solutions, 
while the convention has been able to welcome to its 
meetings Dr. von Rohr, of Jena, who has presented 
a paper on lenses of non-spherical curvature. Many 
members were glad to see the focometer and other 
apparatus and experiments of the president, notably 
the large quarter-wave plates made for the experi- 
ments of Prof. Coker. 
The fact that the portion of the general catalogue 
descriptive of the apparatus of the firms participating 
in the exhibition occupies 350 pages is an indication 
of the hearty support which the industry has given to 
the convention. 
The intention has been to make the catalogue valu- 
able as a book of reference for some time to come 
to persons interested in optics, and also a medium for 
the assistance of the optical industry. For this pur- 
pose a large edition has been printed, and its dis- 
tribution abroad, especially in the Colonies, is 
now under the consideration of a_ special 
committee. The editing has been done at the 
National Physical Laboratory, and Mr. E. H. 
Rayner and Dr. T. M. Lowry have been chair- 
man and secretary of the catalogue committee, on the 
results of which they are to be congratulated, 
especially considering the short time available for its 
compilation. Attention may especially be directed to 
the introductions to many of the classes in the cata- 
logue, which are very valuable epitomes of modern 
methods and apparatus in the most important branches 
of optics. 
A sign of the times is the way in which the class 
devoted to illumination has been supported. Archi- 
tects and engineers have now available not only 
accurate figures for the illumination required in 
different circumstances, but also values for the dis- 
tribution of the illumination produced by the many 
reflectors of various types for use with gas and elec- 
tric light. The use of special types of portable photo- 
meters now available for measuring the intensity of 
illumination leaves no loophole for the unsatisfactory 
and wasteful methods of illumination which have been 
commonly regarded as inevitable. In this connection 
the exhibits of Messrs. Holophane, Ltd., Messrs, 
William Sugg and Co., the Union Electric Co., 
Messrs. Everett Edgecumbe, the Adnil Electrical Co., 
and the Benjamin Electric Co. were a liberal educa- 
