JuNE 29, 1899] 
NATURE 
20t 
Proper registration during the triple printing is secured by 
making reference marks on the plates. A picture of this sort 
once produced can be reproduced indefinitely by making 
contact prints, since the arrangement of the lines will be 
the same in all of the copies as in the original. The 
finished picture is perfectly transparent, and is merely a 
diffraction grating on gelatine with variable spacing. In 
some parts of the picture there will be a double grating, 
and in other parts (the whites) there will be a triple set 
of lines. Having had some difficulty in getting three 
sets of lines on a single film in such a way as to produce 
a good white, I have adopted the method of making the 
red and green gratings on one plate, and the blue on 
another, and then mounting the two with the films in 
contact. It is very little trouble to multiply the pictures 
once the original red-green grating picture is made. 
The pictures are viewed with a very simple piece of 
apparatus, shown in Fig. 4, consisting of a lens cut square 
like a reading glass, mounted on a light frame provided 
with a black screen perforated with an eye-hole through 
which the pictures are viewed. The colours are ex- 
tremely brilliant, and there is a peculiar fascination in 
the pictures, since if the viewing apparatus be slowly 
turned so that its direction with reference to the light 
varies, the colours change in a most delightful manner, 
giving us, for example, green roses with red leaves, or 
blue roses with purple leaves, a feature which should 
appeal to the impressionists. The reason of this kaleido- 
scopic effect is evident, for by turning the viewing 
apparatus we bring the eye into different parts of the 
overlapping spectra. 
It is possible to project the pictures by employing a 
very intense light, and placing a projecting lens in place 
of the eye behind the perforation in the screen. Of 
course a very large percentage of the light is lost, con- 
sequently great amplification cannot well be obtained. 
I have found that sun-light gives the best results, and 
have thrown up a three-inch picture on a four-foot sheet 
so that it could be seen by a fair-sized audience. 
By employing a lens of suitable focus it is possible to 
make the viewing apparatus binocular, for similar sets 
of superposed spectra are formed on each side of the 
central image by the gratings, so that we may have two 
eye-holes if the distance between the spectra corresponds 
to the interocular distance. 
It is interesting to consider that it is theoretically 
possible to produce one of these diffraction pictures 
directly in the camera on a single plate. If a photo- 
graphic plate of fine grain were to be exposed in succession 
in the camera under red, green, and blue screens, on the 
surfaces of which diffraction gratings had been ruled or 
photographed, the plate on development should appear 
as acoloured positive when seen in the viewing apparatus. 
I have done this for a single colour, but the commercial 
plates are too coarse-grained to take the impression of 
more than a single set of lines. With specially made 
plates I hope to obtain better results. 
R. W. Woop. 
NO. 1548, VOL. 60] 
LOCAL UNIVERSITY COLLEGES FOR 
LONDON. 
qe adequate provision of university education for 
London is by no means the simple and straight- 
forward task which some people seem to imagine. From 
whichever of the many possible points of view the question 
of the education of London is considered, the anomalous 
position which has to be assigned to the greatest city in 
the world is the most noteworthy result of the invest- 
igation. If, for instance, an endeavour is made to 
estimate the comparative facilities offered for higher in- 
struction in the metropolis with those to hand in other 
countries and in our own large provincial towns —judged 
on a basis of population—the results arrived at are as 
remarkable as they are interesting and instructive. The 
population of Scotland in 1896 was 4,186,849 ; yet located 
at Edinburgh, Glasgow, Aberdeen and St. Andrews are 
four well-equipped and largely endowed universities ; 
while, in addition to these, is to be found at Dundee 
a college providing university education, and, though 
working with St. Andrews, in receipt of an annual 
grant of 1ooo/. from the Treasury. The population 
of the county of London was last year 4,504,766. If, as 
is done in the University of London Act, 1898, the towns 
within thirty miles of the university buildings are in- 
cluded, the population must be placed at a very much 
higher figure, viz. about six millions and three-quarters. 
So that, keeping well within limits, and running no risk 
of any charge of exaggeration, the inhabitants of this 
metropolitan area may be said to considerably out- 
number those of Scotland. When the universities and 
university colleges provided for this immense population 
are enumerated the total is ludicrously small. There is 
no teaching university, and but three university colleges— 
University College, King’s College, and Bedford College. 
Of course, there are other colleges in London ; but, in 
defining university colleges reference is made to the 
Treasury Minute of June 2, 1897, dealing with the grant 
in aid of the university colleges of Great Britain. 
At University College there were in the faculties of 
Arts, Laws, and Science, in the session of 1895-6, 747 
students, including engineering students. At King’s 
College, during the same session, there were in Arts and 
Science 284 day students, 305 evening students, and 315 
lady students. At Bedford College, the number of 
students throughout the same period numbered 176. The 
total number of persons receiving instruction of uni- 
versity standing in officially recognised institutions was 
consequently not much over 1500 during the year 1895-6. 
If the populations up to date of the eight large towns 
in England provided with university colleges be added 
together, the total obtained is about 3,233,765. Similarly, 
Wales, with a population in 1891 of 1,501,163, has three 
university colleges, now together constituting the Uni- 
versity of Wales. Not only in comparison with Scotland, 
therefore, but also by the side of Wales and the English 
provinces, London is seen to be extraordinarily deficient 
in properly authorised establishments the prime duty of 
which is to provide university instruction. 
It may be urged at this stage that the work of the 
University of London Commission now being performed 
will, as it is intended it shall, completely alter the present 
unsatisfactory aspect of things, and that ere long pro- 
visions which will satisfy the most earnest advocate of 
higher education will be provided. But valuable as 
the coordination of effort which is likely to result from 
the inauguration of the new University of London will 
be, it can hardly be contended that to confer new powers 
upon certain existing colleges, and to rearrange the work 
of the staffs of institutions which have previously proved 
inadequate, will be a complete solution of the proper 
provision of university instruction for nearly seven millions 
of people. 
