174 
NATURE 
[ DECEMBER 24, 1903 
On comparing these days with those on which Bishop’s 
ring was stated to have been visible at Zurich, and with 
the dates, from M. Forel’s paper, of abnormal sunset glows 
seen at Morges, it was found that the successive appear- 
ances of the respective phenomena occurred here about 
twenty days later than they did in Switzerland. Of course, 
the weather conditions at single stations introduce irregu- 
larities, so that the conclusion must be regarded as un- 
certain, but supposing it to be approximately correct, since 
the stations used lie nearly in the same latitude, and we 
can assume that the drift of the elevated dust-clouds was 
from west to east, their velocity in passing around the 
globe, from central Europe to the eastern United States, 
was about 30 miles per hour, or a rate considerably less 
than that found from trigonometrical measurements to be 
the velocity of the highest ice-clouds. 
In the case of the great Krakatoa eruption in 1883, the 
speed of the ash-cloud as it circled the globe from east to 
west along the equator, and its slow diffusion toward the 
poles, was determined from the observation of the successive 
appearances of coloured suns and brilliant sunset glows in 
different parts of the world, collected by the Royal Society’s 
committee appointed in 1884. The assistance in solving 
the problem of atmospheric circulation which a knowledge 
of the drift of dust ejected into the upper atmosphere by 
volcanoes situated in the tropics might furnish would 
certainly justify obtaining all available data bearing on the 
march of the abnormal sky colours. Mr. Clayton, of this 
observatory, began the collection of such data some time 
ago, but was deterred from continuing the work by reason 
of the difficulty in obtaining definite information. <A task 
of such magnitude belongs properly to a commission 
possessing the necessary facilities for collecting and dis- 
cussing the material, so it is hoped that an organisation 
like the Krakatoa Committee, the admirable report of which 
was published in 1887, may undertake the study of the 
recent and present remarkable sky colorations, probably 
occasioned by the eruptions in 1902 of the volcanoes in 
Martinique and St. Vincent. 
A. LAWRENCE Rotcn. 
Blue Hill Meteorological Observatory, Hyde Park, 
Mass., U.S.A., December 11. 
{Internal Oscillation in the Waters of Loch Ness. 
I wou.p beg a little space in your columns to direct 
attention to some of the conclusions which I draw from 
temperature observations taken last summer in Loch Ness. 
Routine observations have been taken at the south-west 
end of the loch several times a day since the middle of July, 
and I find that the temperature at any depth between 100 
and 300 feet changes with time in a markedly periodic 
fashion, the duration of a period being approximately three 
days. At about 200 feet the difference between a maximum 
and a minimum is something like 5° F. At greater depths 
the temperature change is less, but of the same period and 
the same phase. At depths less than 200 feet also the 
temperature change appears to fall off in magnitude whilst 
retaining the same period and phase, but here there appear 
to be other changes more or less obscuring the simple 
periodic variation. Diagram 1 gives a few observations at 
200 feet. 
I conclude from these observations, and others taken at 
different parts of the loch, that there is an internal oscilla- 
tion in the waters—an internal seiche, similar to the swing- 
ing which may be set up in the interface between oil and 
water lying the one above the other in a trough. For such 
a motion we require liquids of different density lying one 
above the other; in the loch the upper waters being warmer 
are lighter than the lower strata, and I think it probable 
that the region where the temperature changes most 
abruptly acts as a surface of separation, and is comparable 
with the interface between the oil and water in the simple 
arrangement just mentioned. In Diagram 2 I have tried 
to illustrate the motion. The shaded portion is intended to 
represent the warmer water, and the hard line the region 
where the temperature changes most abruptly. Rough 
calculations on the assumption that the swinging is of this 
nature give the period of the order observed. A very re- 
NO. 1782, VOL. 69] 
markable point is the large amplitude of the vibration. At 
the ends of the loch the isothermal surfaces suffering the 
greatest displacement may move through as much as 75 
feet. 
The observations make it probable that this swinging is 
started by gales and strong winds. Winds produce a slope 
of the upper isotherms down towards the lee end of the 
loch, and the stronger the wind the deeper is this effect felt. 
So that strong winds are able to displace the relatively deep 
oct ioe Be 47 46 45 44 
20 
21 
22 
23 
24 
25 
Fic. 1. 
isotherms in that region where they act as an interface, 
and on the wind falling the isotherms swing back and 
continue to swing freely with a natural period. 
Unfortunately it is necessary to wait for the return 
of summer before more observations can be made bearing 
on the subject, as the waters are now of almost uniform 
temperature. 
I believe I am right in saying that such a phenomenon 
had up to this never been even suspected by limnologists. 
I do not think the temperatures of the deeper strata of water 
in any lake have been systematically observed. The pheno- 
menon seems to me of great interest and worthy of careful 
study, as it appears to rank in importance along with the 
ordinary seiches which have been studied with such care 
and perseverance by Forel and others. 
E. R. Watson. 
Scottish Lake Survey, Fort Augustus, N.B., December 12. 
