204 
isolated, band of light across the zenith, but as soon as it 
was dark that evening, the zodiacal light was distinctly 
seen to stretch across the whole sky, forming that faint 
band of light previously observed ; I then began to note 
its position, but the best observations were made on the 
night of the 27th, when it was most distinct. 
On that night it passed centrally over the planet Venus, 
and then over the stars 6 Capricorni, y Aquarii, o Piscium, 
and reached a point between the Pleiades and the 
Hyades, so that the central portion of the light traced out 
the course of the Ecliptic with wonderful precision ; it 
was brightest in the central part of the band, and gradu- 
ally faded off towards the edges; its illumination about 
Venus was somewhat greater than that of the Milky Way, 
but became fainter and fainter as the light proceeded 
along the Ecliptic ; it was impossible to trace it beyond 
the Hyades, where it seemed absolutely to terminate ; at 
midnight, however, a feeble glow could be seen above the 
eastern horizon in Leo and Cancer, but nothing was cer- 
tain about this branch. 
Returning to the western and brighter branch, at Venus 
its breadth was about 40°, and as the longitude of the 
planet was 280° while that of the sun was 246°, its breadth 
was 40° at a distance of 34° from the sun; at 8 Capricorni 
its breadth was 20°, at y Aquarii 16°, and at o Piscium 
10°, so that we get the following results :— 
Distance from sun Breadth 
BAC ATS Be Seat wate eAOr 
GORE Sak Ue eo 
OZiaba Ye Cena 
TAQ) Is at ns A MY Ae oTO 
and its extreme distance from the sun was about 177° 
where it was too faint to note anything but its existence. 
The light seemed perfectly fixed in the heavens, and 
there was no sign of any displacement such as might be 
caused by parallax combined with the earth’s rotation ; 
and when the brighter part had set and was far below the 
horizon, the band across the zenith was quite as distinct 
as before. 
Now these few facts go a long way towards explaining 
the nature of the zodiacal light, and a few more observa- 
tions at different times of the year may be all that are 
necessary to do so satisfactorily ; but as the light was so 
vivid here, it must have been seen in other parts of the 
world, and a comparison of the different accounts may 
bring about the desired result; hence these notes, and 
the following rough explanation. 
The zodiacal light has generally been supposed to be 
a luminous ring, surrounding the Sun, and situated 
between the orbits of Venus and Mars ; the fact that the 
light has often been seen in both the east and west at 
the same place and time does not affect the probability 
of this explanation, as we have only to suppose the 
earth to be just within the ring; but there are many 
difficulties to encounter, and the explanation never seemed 
satisfactory. The instant, however, that I saw the pro- 
longed ray, I felt sure that the zodiacal light was similar 
in its nature to the rays issued from a comet towards the 
sun, which, drifting over the nucleus, are then forced 
backwards and form the tail; and that in the case of 
the earth, the light is generated in those regions to which 
the sun is vertical, and passing round the earth, the light 
is swept back in a direct line from the sun, thus forming 
a train which always tends towards a point in the heavens 
180° from the sun, and which is therefore stationary with 
regard to the earth’s axial rotation. 
It is not easy, however, to test the truth of these ideas 
by means of the notes above, but the following attempt 
may not prove uninteresting. 
_ Ifthe zodiacal light were a ring, and the earth within 
it, we could compare the distances of the different parts 
of the ring by means of their apparent angular breadths, 
supposing the actual breadth of the ring to be uniform : 
NATURE 
en ee ee 
in order to see whether that prolonged Tay was part of a! 
| Fan. 36, 1873 
ring or not, let E S be the line joining the earth and the 
sun, the plane of the paper coinciding with the Ecliptic; — 
and at an angle of 34°(6,) measure off any length EA 
(7,), in which direction the breadth of the light was 40° 
(,) ; now, the distance 7, of any point where the angular 
breadth is ¢,, will be determined by the equation— 
7, = 7, tan Be: cot Po 
2 2 
so that we can draw EB, EC, and E D, corresponding 
to the}second, third,Jand {fourth observations ; but ‘the 
curve drawn through these points is by no means an arc 
of acircle, and very fairly represents what we have ex- 
pressed in words above, so that the rays issuing from E 
towards S are swept to the right hand and to the left, 
and passing by the earth they form a train of light 
stretching out into space, 
But to what an astonishing distance must this train 
proceed, in order to acquire an angular distance of 177° 
from the sun! It is, however, quite possible that the two 
branches close together near the point F, following the 
dotted curves ; these curves are the positive and negative 
branches of the spiral of Archimedes, and fairly repre- 
sent our curves for an angular distance of 90° from the 
sun. MAXWELL HALL 
Jamaica 
THE LATE PROFESSOR W. F MACQUORN 
RANKINE 
THE death of Prof. Macquorn Rankine, which we 
announced a fortnight ago, will excite a pang in 
the hearts of many persons who had enjoyed actual in- 
tercourse with the genial spirit whose early loss we now 
mourn, and of a still greater number who were only 
acquainted with him through his. published works, He 
died at his residence in Glasgow, on Christmas Eve, 
in his fifty-third year, the date of his birth being July 5, 
1820, For several months he had been labouring under a 
serious derangement of his eyesight, coupled with heart 
disease ; but it was confidently hoped for atime that hisvalu- 
able life might be preserved for the benefit of science, pro- 
vided that he rested himself from all his ordinary labours. 
Latterly he did take that rest which seemed to be so im- 
peratively demanded by his physical nature, the chief 
portion of his ordinary work, namely, that of conducting 
his class in the University of Glasgow, being handed 
over to Mr. Bamber, C.E., who formerly distinguished 
himself as a student under the deceased professor ; but 
the bodily system had evidently little power of resisting 
the ravages of the insidious disease under which it 
laboured ; paralysis set in on Sunday, the 22nd ult., and 
in forty-eight hours Macquorn Rankine was dead. 
The amount of space at our disposal is quite insufficient 
for the simple mention of the many important facts that 
Pe Ee oe ah wh hs Cale 2 eek ee 
: 50 Fae > ees 
