JUNE 27, 1912] 
Tur Brazivian Ecuirse on Ocroser 10.—In two 
letters to Mr. Chambers, published in the May 
number of the Journal of the British Astronomical 
Association, Mr. Harold Thomson gives some par- 
ticulars concerning the October weather (1910), the 
local conditions, &c., in the neighbourhood of Rio. 
Observers who intend to go to Brazil in October 
next will probably find some useful hints concerning 
the journey, &c., in these letters. 
THe ASTRONOMICAL AND ASTROPHYSICAL SOCIETY OF 
America.—The papers read at the meeting of this 
society held at Washington in December last are 
reported in abstract in No. 905 of Science. A com- 
parison of Dr. Peters’s celestial charts with four of 
the photographic charts of the sky taken at Bordeaux 
and Algiers led Mr. J. G. Porter to the conclusion 
that they contain, on the average, 50 per cent. more 
stars than the photographic charts, which are, there- 
fore, by no means complete to the twelfth magnitude. 
Dealing with the moon’s parallax, Dr. F. E Ross 
finds the mean distance to be 238,8579+11 U.S. miles 
and the semi-diameter to be 1,079°93+1'04 miles; the 
density, in terms of that of the earth, is 06043 + 0°0003. 
The subjects of many of the other papers have already 
been dealt with in these columns. 
THE OPTICAL CONVENTION, 
THe Optical Convention of 1912, which was yes- 
terday brought to a successful conclusion, has 
rightly awakened widely extended interest in scien- 
tific circles. The use of optical methods of investiga- 
tion is so universal and it so nearly affects research 
in all directions, that there is no body of scientific 
men who can afford to be indifferent to the successes 
of the makers of optical instruments and to the re- 
searches of those who are occupied with designing 
them. Hence the widespread interest which has been 
manifested in the proceedings of the Optical Conven- 
tion, and the large measure of success with which 
its meetings and other proceedings have been con- 
ducted. 
The convention was opened on Wednesday, June 
19, by an inaugural address delivered by the presi- 
dent, Prof S. P. Thompson. A graceful preliminary 
ceremony was performed by Mr. C. P. Trevelyan, 
1912. 
M.P., who, speaking in behalf of the President of | 
the Board of Education, welcomed the president and 
members of the convention to the Science Museum 
and the Imperial College, expressing in felicitous 
phrases the interest which his Majesty’s Government 
has been taking in the realisation of the plan for 
holding an Optical Convention. The official welcome 
was repeated on the following day, when the Director 
of the Science Museum, addressing the members of 
the convention assembled to meet him, explained that 
the idea of providing suitable accommodation for the 
proceedings of such a gathering formed part of the 
settled policy of the department in connection with 
the rebuilding of the museum. 
It will be matter of satisfaction to all who have 
the interests of science at heart to know that the 
Board of Education has adopted so enlightened a 
policy, and it is perhaps to be counted a very for- 
tunate circumstance that at this particular time, 
when the plans for rebuilding the museum are under 
consideration, the experiment of holding a congress 
of scientific men within the walls of the museum 
should be carried through. It has been made abun- 
dantly evident by that experiment that great advan- 
tages can be secured in that way. The educational 
purposes of the museum are never better served than 
when its resources are placed at the service of those 
No. 2226, vot. 89| 
NATURE 
433 
| who are actively engaged in prosecuting the studies 
| to which the collection itself is subservient. The 
convenience of being able to supplement their own 
resources by drawing upon the resources of the 
museum has been very evident to the committee 
engaged in organising and carrying through the 
_ work of the convention. It can scarcely have been 
less satisfactory to the Board of Education and to 
| its officers to see their collection of scientific objects 
| turned to the best account by the assembly within 
the walls of their building of so large a number of 
expert persons to whom those objects are objects of 
scientific interest. We are glad to see that the ex- 
periment of providing such accommodation for the 
meeting of the convention has been carried through 
with so large a measure of success as to justify the 
hope that it may be repeated hereafter in various 
forms and on many occasions. 
Turning now to the proceedings of the convention, 
one naturally inquires first of all as to the steps of 
progress which are registered in connection with this 
meeting. Accepting the lead of Prof. Thompson’s 
very able inaugural address, one is led to think of 
the subject of illumination as that in which the most 
rapid advances are being made at the present time. 
These advances are well illustrated in the exhibition, 
where the illuminating engineers are very much in 
evidence, while in the lecture-rooms, although they 
have been perhaps not quite so much to the fore, 
they have very distinctly made their influence felt. 
It may indeed, be said that with respect to general 
illumination, the lighting, for instance, of streets and 
rooms, whether artificially or from natural sources 
of light, theory is at present in its cradle and even 
experiment in its initial stages. Much, however, has 
been already done, and still more may be expected 
to be accomplished within the next few years, if the 
present activity of investigators and inventors along 
this line should be maintained. The illumination 
suitable for optical instruments, and particularly the 
problem of illumination of objects under microscopic 
examination, has long been a subject of study. But 
here also we seem to be upon the crest of a wave. 
New methods of controlling the illumination of the 
stage of the microscope and new rules for interpret~ 
ing the appearances presented in an illuminated field 
are occupying the earnest attention of investigators 
and with results which appear to be full of the promise 
of future achievement. 
While the problems presented by illumination 
appear to be the direction in which research along 
optical lines is just now most conspicuously success- 
ful, the problems relating to the imagery of move- 
ment appear, on the other hand, to be those in which 
invention has made its most sensational advances. 
Prof. Thompson, who gave his audience some very 
interesting statistics concerning the astonishing popu- 
larity which kaleidoscopes and stereoscopes obtained 
when they were first introduced to the public, was 
able to add that since the date of the last Optical 
Convention, now seven years ago, the developments 
of the kinematograph had drawn from the public a 
thousand times as much money as either of those 
inventions. The inventors in this department would 
seem indeed to be too busy making their fortunes to 
have any time or interest to spare for the Optical 
Convention, and we observe that nothing in the 
nature of modern kinematography was on view in the 
exhibition. 
Perhaps the time has scarcely come yet for the 
reduction into the terms of exact science of the 
theory of moving images. The elements of such a 
theory have been available, although in an uncon- 
nected form, to visitors to the Optical Convention. 
| But the principles of image combination, the effects 
