wOlZ 
NATURE 
[AuGUST 15, 1912 
stallation, and does not appear yet to have been 
very much used over here. 
In order to be really valuable, the resemblance 
to daylight should be very exact. Various special 
screens have been used with enclosed arc lamps 
as ‘daylight lamps,” but the difficulties in secur- 
ing a permanent and trustworthy screen are con- 
siderable. One method consists in selecting and 
superimposing suitable blue and green glasses, 
but it is generally recognised that to imitate the 
spectrum of natural light with precision a gelatine 
screen must be included. A method that has 
recently been described by R. B. Hussey,” in the 
United States, is to mount the coloured glasses 
side by side and to place underneath a diffusing 
glass screen, which serves to mix the components 
into an approximate white light. A similar de- 
vice has been used by C. H. Sharp and P. S. 
Millar in an emergency in order to secure an ap- 
proximate result at a florists’ exhibition.” Ives and 
Luckiesh have concentrated their efforts on the in- 
vention of a form of screen which can be applied 
with a tungsten incandescent lamp, and thus con- 
veniently used on an ordinary lighting circuit. 
They found it necessary to use both cobalt blue and 
signal green glasses and a special gelatine filter, 
and appear to have obtained very successful results. 
The most recent achievement in this directon 1s 
that of Dr. Kenneth Mees, described before a 
meeting of the Illuminating Engineering Society in 
London this year. By a combination of gelatines, 
involving the use of a newly discovered blue dye, 
he states that a very perfect resemblance to day- 
light is secured, and that the results are remark- 
ably permanent. The absorption of light is natur- 
ally considerable (amounting to about 85 per cent.), 
but for the special work for which this lamp is 
intended such a loss in efficiency is not of very 
great consequence in comparison with the advan- 
tage of being able to extend the hours of work 
after daylight has ceased. 
It is not suggested that lamps of this kind would 
come into general use as a substitute for artificial 
illuminants of the ordinary kind. Indeed, the im- 
pression is that people rather prefer the more golden 
hue of artificial light in the evening. This hue 
has become mentally associated with comfort, and 
possibly it serves to carry out the sequence of tone 
from daylight to the warmer tones of sunset. The 
idea is rather to use these artificial daylight units 
for special purposes. For example, it would doubt- 
less be of value in a drapers’ establishment to 
have a small recess illuminated in this way, so 
that customers, in choosing materials, would be 
able to compare their colours under this light with 
their appearance by the ordinary artificial illumin- | 
ants. 
There is one question that has an important 
bearing on these problems, namely, the difficulty 
in decidine on a standard white light. The re- 
searches of Dr. Nichols at Cornell University have 
shown that the spectrum of daylight varies con- 
siderably with different climatic conditions and at 
different altitudes. In a town especially, where 
2 Trane, Amer. Ilum. Engin. Soc , February, rgr2. 
NO. 2233, VOL. 89] 
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| Petersburg ; 
periodical fogs give the transmitted light a more 
ruddy character, this is so. But in the country 
it appears that throughout the greater part of 
the day the quality of light from a white sky does 
not vary very greatly, and delicate colour-work 
would usually be done under these conditions. 
THE DUNDEE MEETING OF THE 
BRITISH ASSOCIATION. 
see following is a list of the American, colonial 
and foreign guests who up to the present date 
have accepted invitations to attend the forthcoming 
meeting of the British Association at Dundee. It 
will be seen that the number is unusually large, and 
indicates a gathering of scientific men from abroad 
far beyond anything that has taken place at recent 
meetings of the Association. 
Prof Aganassief, St. Petersburg; Prof. Allardice, 
Leland Stanford; Prof. Frank Allen, Winnipeg; 
Prof. Raoul Anthony, Paris; Prof. Leon Asher, Bern; 
Dr. Baglioni, Rome; Prof. Ch. Barrois, Lille; Dr. 
Becker, Brussels; Prof. J. J. Borgmann, St. Peters- 
burg; Prof. Dr. Botazzi, Naples; Dr. Burgli, Bern; 
Prof. Burton-Opitz, New York; Prot. Irvine 
Cameron, Toronto; Prof. D. H. Campbell, Cali- 
fornia; Prof. C. Chilton, Christchurch, New Zealand; 
Prof. Archibald Clark, Winnipeg; Prof. Franz Doflein, 
Freiburg; Dr. J. Drugmann, Brussels; Prof. Fano, 
Florence; Dr. G. W. Fields, Boston, Mass.; Prof. 
J. C. Fields, Toronto; Miss Alice Fletcher, Cam- 
bridge, Mass.; Prof. Dr.-Max v. Frey, Wurzburg; 
Dr. A. Gérardin, Nancy; Prof. A. Gerschun, St. 
Prof. E, Gley, Paris; Dr. Gotham, 
Dr. Gottlieb, Heidelberg; M. Yves 
Guyot, Paris; Prof. F. Haber, Karlsruhe; Dr. 
W. 4H. .Hale, New York; Prof. Hamburger, 
Groningen; Prof. Paul Hanus, Cambridge, Mass. ; 
Prof. Emil Haug, Paris; Mr. C. Hedley, Sydney; 
Prof. Paul Heger, Brussels; Prof. S. E. Henschen, 
Stockholm; Prof. Dr. A. F. Holleman, Amsterdam; 
Mr. Hans Holzwarth, Mannheim; Prof. Hubrecht, 
Utrecht; Prof. Ida Hyde, Kansas; Prof. Ch. Julin, 
Liége; Prof. H. Jungersen, Copenhagen; Prof. H. 
Kayser, Bonn; Prof. F. Keibel, Freiburg; Prof. 
A. E. Kennelly, Cambridge, Mass.; Prof. Dr. A. 
Kossel, Heidelberg; Prof. Kélpin-Ravn, Copenhagen ; 
Dr. Kramp, Copenhagen; Prof. Kronecker, Bern; Prof. 
Berlin; Prof. 
Kuliabko, Tomsk; Prof. F. Lindemann, Munich; 
Prof. Lindmann, Stockholm; Dr. Otto Lipman, 
Berlin; Prof. Dr. Loewi, Graz; Dr. F. Lohnis, 
Leipzig; Prof. Maurice Lugeon, Lausanne; Prof. 
A. -B> Macallum, F.R-S.; Toronto; Prof. JayjzeR= 
Macleod, Cleveland, Ghio; Prof. J. C. McLennan, 
Toronto; Prof. F. Mall, Baltimore; Prof. Gustav 
Mann, New Orleans; Prof. S. J. Meltzer, New York; 
Dr. Hans Meyer, Vienna; Prof. R. A. Millikan, 
U.S.A.; Prof. E. C. Moore, Yale; Mr. T. Mortensen, 
Copenhagen; Baron F. Nopsca, Hungary; Dr. C. H. 
Ostenfeld, Copenhagen; M. Paul Otlet, Brussels; 
Prof. @yen, Christiania; Dr. Ove Paulsen, Copen- 
hagen; Prof. C. A. Pekelharing, Utrecht; Dr. 
C. G. J. Petersen, Copenhagen; Prof. Maurice 
Philippson, Brussels; Prof. B. Osgood Pierce, 
Harvard: Prof. F. H. Pike, New York; Dr. A: 
Pitter, Bonn; Dr. Redeke, Helder; Dr. Reusch, 
Christiania; Prof. L. Rhiimbler, Hann-Miinden; Dr. 
Sahli, Bern; Prof. J. Schmidt, Copenhagen; 
Prof. J. W. Spencer, Washington;: Dr. von 
Sustschinsky, Munich; Dr. Emil Tietze, Vienna; Dr. 
Th. Tschernyschew, St. Petersburg; Prof. Max 
Verworn, Bonn; Prof. Swale Vincent, Winnipeg; 
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