
Aug. 31, 1871] 
NATURE 
345 

moon and full moon, at the boundary plane appertaining to the 
moon. The result is that all parts of the mass are perpetually 
undergoing considerable cross-strains, for the forces of tension 
and compression will not relieve each other, as they act at right 
angles to one another. 
If the mass of the earth were not rigid, but sufficiently 
elastic, like, for instance, a globe of india-rubber, the particles 
would yield to their small disturbing forces ; and the result would 
be that each particle, as it arrived by rotation at each point of its 
circuit, would move in proportion to the force acting on it, one 
way or the other. In this case there would be nothing to cause 
the axis to move ; the earth would steadily revolve, and no pre- 
cession or nutation would occur. The whole mass would, as it 
were, breathe, heaving its surface and drawing it in again in a 
complicated undulation. 
But observation shows that the earth /as precession and 
nutation ; and therefore the mass cannot be thus elastic. 
If it be only partially rigid, then there would be a correspond- 
ing degree of yielding ; but precession and nutation would still 
be produced, and a strain, in a somewhat diminished degree, 
affect the mass 
Now, mathematical calculation made on the hypothesis of 
the earth’s mass being absolutely rigid, and that throughout, 
shows that the annual precession would be 51°3566".* Astrono- 
mical observation shows that the precession is actually 50°1”. 
The remarkable nearness of these results is sufficient proof that 
the earth’s mass is not the limp thing some take it to be; all 
viscous-fluid from only 100 miles down to the centre, moving so 
slowly, that it gives inertia to the hard crust (supposed thin) as 
if it were all solid! It is more like the highly rigid mass which 
Sir William Thomson has shown it to be from other conside- 
rations. Joun H. Pratr 
Calcutta, July 15 
Meteorology in South Australia 
As it may be interesting to some of your English readers to 
hear something of natural phenomena in such an out-of-the-way 
part of the world as South Australia, I forward a description of 
three very fine meteors which have lately been seen here, as well 
as a splendid display of Aurora Australis. 
On January 5th, 1871, at about half-past nine r.m., I observed 
a splendid meteor. It appeared at first like a fixed star about 
three times as large as Jupiter, or say six or seven inches in 
diameter, and was probably about 15° above the horizon, or nearly 
of the same apparent height as a large star which was just below the 
planet Jupiter, a little to the west of him and within half an hour 
of the meridian. The meteor, which was very brilliant, somewhat 
of the appearance of Jupiter, remained apparently stationary for, 
at least, five seconds ; it then gradually began to moye from a 
due north position to a direction about S.S.E., and in a horizon- 
tal line ; it then burst into several smaller meteors and went out, 
having lasted fully twenty seconds altogether. The moon was 
shining brightly at the time, being a few days off the full. 
On the same night, and at about the same hour, a large meteor 
was seen by a survey party at Hookina, a place about 400 miles 
north of Adelaide. The surveyor in charge of the party (Mr. 
Hamilton) from whom I obtained the particulars of this meteor, 
says he was facing the east when he observed it going from N. E. 
to S.E., describing a large arc at an apparent elevation of 20°. 
He describes its colour as greenish, and so bright that it almost 
overpowered the light of the moon. It ultimately burst with a 
loud explosion into a number of fragments of red and blue 
colours, and the earth was felt to tremble as though a shock of 
an earthquake had occurred. 
On the 25th March last, at about twenty minutes to three 
o’clock in the afternoon, I observed a meteor in the full blaze of 
thesun. It appeared like a bright brass-coloured ball of fire, 
shooting through the sky like arocket ; it seemed to havea green 
and blue light round a central brass-coloured nucleus. The 
meteor appeared about three inches in diameter ; it hada whitish 
comet-like tail, about three feet long, and it came from the 
N.N.E. and travelled downwards towards the S.S.W., so that 
as I was looking south it appeared to come over my left shoulder. 
It lasted about ten seconds, then burst without noise, and became 
dissipated. This meteor seemed to fall at about 15° from the 
horizon. 
In the S. A. “ Register,” a few days after seeing the last 
*~ See this worked out in my ‘‘ Mechanical Philosophy,” 1st edit. p. 562, 
and edit. p. 549. 

described meteor, ‘it was stated that a surprising sound was 
heard at Point Macleay, and other places about fifty or sixty miles 
to the south-east of Adelaide as of the firing of cannon, and the 
correspondent of that paper at Mannum (a place on the River 
Murray, about sixty miles east of Adelaide) writes as follows :— 
**On Saturday last (25th March) at exactly 2.45 p.m., I was 
looking down the Murray River, when suddenly my attention was 
attracted by a large ball of fire falling from the heavens in almost 
a perpendicular course. The lakes are from here in the direction 
which it indicated—almost due south—so that I have no doubt 
the extraordinary phenomenon mentioned as having occurred on 
the shores of Lake Alexandrina, may have arisen from one of the 
causes assigned, viz., a falling meteor or an aerolite. What I 
saw was evidently the explosion immediately preceding the fall, 
and it presented the appearance of a luminous meteor.” ... . 
The display of ‘‘aurora australis’? which I observed on th 
23rd March last, commenced at about eight o’clock p.m. It 
increased in brightness till eleven o’clock, when it gradually faded 
away. Atabout two o’clock A M.,while at a ball, Icame out on 
the balcony and observed the whole southern sky lighted up by 
a most gorgeous display of aurora. It occupied about 70° or 
80° of the horizon, extending from about S.S.E to S.W., and 
reached to a heightof say 60° above the horizon. It was of a 
splendid red rose colourand streaked with beams of white light 
at various distances apart—say two bands of white in every 10°. 
These white bands appeared about two feet to five feet wide, 
which would answer to say 5° observed by the eye alone. The 
display was so bright that by placing my hand with the fingers 
apart at about two feet from a lady’s white dress, I could dis- 
tinctly see the shadow of each finger. This aurora was also seen 
in Victoria and New South Wales. 
I may mention that Adelaide is situated in south latitude about 
35°, and longitude 138° 40’ M. M. FINNIsS 
Adelaide, June 19 
The Solar Aurora Theory 
In the very interesting lecture of Mr. Lockyer upon the recent 
solar eclipse which has just appeared in NATURE, he says, 
speaking of the green line layer above the hydrogen, ‘‘ Here 
obviously we have, I think, merely an indication of another 
substance thinning out, in spite of the extraordinary suggestion 
which was put forward that the corona was nothing but a fer- 
manent solar aurora.” 
I agree entirely in this view except as to what would seem to 
be implied by the expression 77 sfite of. I fail to see any incon- 
sistency between the idea of a substance “‘ thinning out” and a 
permanent solar aurora, 
What I intended in adopting and endorsing this auroral hypo- 
thesis was simply this : to express the belief (which I still hold, 
though with no great tenacity) that the substance which com- 
poses this green-line layer is also found in the upper regions of 
our atmosphere in a state of almost inconceivable tenuity, and at 
an elevation of certainly more than one hundred miles ; and, 
further, that the peculiar filamentary and radiant structure of the 
corona, and very possibly its luminosity to some extent, are due 
to solar forces closely analogous to those which produce our 
terrestrial auroras. 
Or in other words, that an observer, at the planet Mars for 
instance, looking at the earth during a period of auroral activity 
would see its poles capped by a corona in substance, structure, 
and to some extent in origin, closely analogous to that which is 
permanent around the sun. 
And if we grant the identity of the 1474 line with that which 
is, to say the least, so closely coincident with it in the auroral 
spectrum, it is difficult to see.why the hypothesis should be con- 
sidered ‘‘ extraordinary,” or fev se improbable. 
That the enormous chemical, thermal, luminous, and magnetic 
activity of the solar surface should be unaccompanied by mani- 
festations of what we call electric energy seems far more unlikely 
than the contrary ; and if such energy operates we should naturally 
look for phenomena, the counterparts of those by which it shows 
itself here, but on the so/ay scale of course. 
As to the identity of these lines, however, there may fairly 
remain some doubt. This line in the spectrum of the aurora is 
so rarely seen, so faint, and so difficult of observation, that, al- 
though the few observations thus far obtained show even a sur- 
prising agreement with each other and with this idea, it is safer 
to maintain a cautious reserve. C, A, YOUNG 
Dartmouth College, U.S.A., August 16 
