999 
NATURE 
[JULY 29, 1915 

maximum, it did not even complete the one transit 
as a spot group, but merely as a faculic area. 
Now this particular disturbance was presently accom- 
panied by quite a number of others, which passed 
through similar stages of rapid growth, and in some 
cases of decay. Thus the southern activity belt, which 
had just previously been decidedly quiescent, showed 
within a few days no fewer than five distinct outbreaks 
extending over a longitude of some 140° or less (June 
16), to which yet another was added by June 21, 
while in north latitude we had some four outbreaks, 
amongst which two formed the largest then on view. 
The simultaneous eruptive paroxysms witnessed 
from June 13 to June 24 were so numerous that to me 
it appears utterly futile to endeavour to link a par- 
ticular magnetic disturbance during those days with 
any of these scores-of violent commotions. With such 
a multiplicity of intensely active foci scattered over 
the sun’s disc all that can be safely claimed is to point 
to an undoubted abnormal magnetic terrestrial condi- 
tion coincident with an abnormally active sun. 
In Nature for July 15 you give an interesting report 
of a fine aurora having been seen by Prof. Barnard 
at Yerkes Observatory in the night of June 16-17. 
Mention has also been made of a sudden: magnetic dis- 
turbance as early in that month as June 7, by Dr. 
Chree, but I see no report from these two observers 
as regards a very fine auroral display which a trust- 
worthy Canadian observer has reported to have taken 
place late in the evening of June 12. The same Cana- 
dian observer also witnessed the display of the 
evening of June 16, and there can be therefore no 
confusion of dates. I wish to lay emphasis on the 
auroral display of the night from June 12-13, because 
it practically coincided with the explosive development 
of a spot-outbreak near the east limb, which I wit- 
nessed in the early morning hours of June 13. The 
Greenwich (and other) photographs will bring the 
proof of the quite unprecedentedly quick development 
and decay of that particular solar outbreak, which 
reached a stupendous magnitude within less than two 
days in an abnormally low iatitude, and accompanied 
by a display of activity, as witnessed through the 
spectroscope, of an intensity rarely seen. 
ALBERT ALFRED Buss. 
““Barrowdale,” 22 Egerton Road, Chorlton- 
cum-Hardy, Manchester, July 18. 

Cement for Polarimeter Tubes. 
In Nature of February 25, 1915, was printed a 
letter from me requesting suggestions for a cement 
suitable for fastening the end discs of polarimeter 
tubes in such a way as to resist the action of organic 
liquids at high temperatures. Several gentlemen 
kindly wrote to me privately making useful sugges- 
tions, and it may perhaps be of value to someone else 
engaged upon similar work if I mention briefly what 
these suggestions were. 
Mr. O. L. Brady, of the Imperial College of 
Science, proposed fused silver chloride. Mr. Wm. 
Doran, Liverpool University, describes a zinc oxy- 
chloride cement, and another made by mixing a thick 
mucilage of gum acacia with calomel. Dr. Pickard 
suggests litharge and glyceric acid, but adds “that 
there seems to be some trick in regard to its applica- 
tion.” Mr. Thomas Steel, of the Colonial Sugar 
Refining Co., Sydney, N.S.W., in a letter which the 
editor has forwarded to me, describes a preparation he 
has used for many years for cementing glass tubes 
into metal holders, etc. ‘“‘A soft putty is made of 
litharge and glycerine, and used just like plaster of 
Paris, allowing about sixteen hours for setting. The 
hard-set compound resists water, oil, or alcohol, and 
is quite air-tight.’ I believe that a mixture of gela- 
NO. 2387, VOL. 95| 

tine and acetic acid is also used as a cement, but to 
what extent it is resistant I do not know. 
Another ingenious method of making a good joint, 
due, I understand, to Prof. W. Ostwald, was recom- 
mended to me, curiously enough, by M. le docteur 
Dolne, of Liége, a visitor amongst us on account of 
the war. By covering the centre of the disc with 
wax, and then immersing in an ammoniacal silvering 
solution, an annulus of silver is deposited on the 
disc, where it would come in contact with the end 
of the tube; the ends of the glass tube are treated 
similarly, Alternatively a deposit of platinum-black 
may be produced by moistening with platinum 
chloride solution and subsequent heating. The discs 
are then placed in position, the tube filled with a 
suitable silver or gold solution, one of these metals 
being then deposited electrolytically on the surfaces 
already silvered, or platinised, until the joint has 
become perfectly tight. The only question which 
might arise in regard to this seal is that, on heating, 
the different expansion of the glass and the metal 
might possibly cause leakage. 
As the resisting power of most of these cements 
could not be definitely guaranteed by their suggesters, 
and the investigation of them all would constitute 
practically a research in itself, I followed the line of 
least resistance, and have tried, in the first place, a 
commercial preparation, **Cazmentium,” recommended 
to me by Dr. J. R. Henderson, of the Royal Technical 
College, Glasgow. This is prepared by the Camen- 
tium Co., Ltd., Tanner Street, Bermondsey, London. 
Two tubes cemented with this material have stood 
well so far, resisting the action of boiling water and 
of some organic liquids up to temperatures of about 
150°. A third broke down in the same circumstances, 
but was perhaps not properly cemented. I propose to 
try some of these other cements as occasion may 
require. In the meantime, any readers of NATURE 
seeking for such a substance may find amongst these 
suggestions one likely to be suitable for his particular 
purpose. I should like, in conclusion, to thank the 
gentlemen who have so kindly assisted me with their 
proposals. T. S. PATTERSON. 
Organic Chemistry Department, 
University of Glasgow, July 15. 

Experiment on Sunset Colours. 
EVERYONE is more or less familiar with the coloured 
halo around a light when viewed through a bedewed 
window, and the streaks of colour which a cloud of 
vapour presents in a strong light. The purity of 
colour in the diffraction halo depends essentially on 
the uniformity of size of the condensed droplets, and 

the same remark may be applied to a cloud or mist. 
It occurred to me that the colours of a mist or cloud 
could be made more brilliant and extensive by con- 
trolling in some way the motion and distribution of 
the differently sized suspended droplets. I have 
accomplished this partially by the following apparatus. — 
The cylindrical surface of a tin can A was wrapped 
closely with a sheet of thick blotting paper and sup- 
ported in an upright position. A board B about 2 ft. 
square, with a central hole in it, was fitted over the 

