236 
NATURE 
1 a z 
[Fuly 21, 1870 
Are Jupiter’s Cloud-belts due to Solar Heat ? 
A CIRCUMSTANCE which, so far as I know, has not yet been 
noticed, seems to ine to afford very strong evidence in favour of 
my theory that the cloud-belts of Jupiter are caused by heat ex- 
isting in the planet itself. If the cloud-belts were caused by 
solar heat, they should exhibit a characteristic corresponding to 
what is observed in the case of the earth’s equatorial cloud-zone. 
“© At the equator,” Kamtz remarks, ‘‘ the sun nearly always rises 
in a clear sky ; towards mid-day the heavens are clouded ; to- 
wards evening the clouds disperse.” Now it follows that to an 
observer regarding the earth as we see Jupiter, there would 
appear at all times only a fragment of an equatorial belt, near the 
middle of the disc. But the belts of Jupiter present no such 
fragmentary appearance ; there is a change in their aspect close 
by the edge of the dise, but the change is one obviously arising 
from the foreshortening. 
Another circumstance also is worth noting. If the cloud- 
belts of the outer planets were sun-raised, the great tropical belt 
of Saturn ought to follow the sun as the tropical calm zone of 
the earth does. ‘The fact that the Saturnian belt remains per- 
sistently equatorial is very significant. Ricup. A. PROCTOR 
The Rotundity of the Earth 
In your number for July 14th, after publishing an ex parte 
statement, you ask, ‘Will nothing stop Parallax’s mouth Tae oe 
hope you will allow me to say, in your next issue, that only one 
thing can operate in doing so! That one thing is a practical 
experiment fairly conducted, honestly reported, and logically 
applied. Your readers will notice that although my signature 
(Parallax) is appended to the ‘‘ copy of agreement,” it does not 
appear in the ‘‘ copy of certificate,” and it is proper they should 
know the reason. It had been agreed that the flags should be 
fixed in my presence, and that the spirit-level employed should 
be in good working order and to my satisfaction in every respect. 
On arriving at the ‘‘scene of operations ” at the appointed 
time, I found that the flags had been fixed, and that the spirit- 
level had been adjusted for some time before my arrival. I 
immediately protested, and demanded that I and the friends with 
me should go and measure the altitude of each flag, but an obsti- 
nate resistance was offered to this, and also to any interference 
with the adjustment of the “‘ level.” I therefore at once declined 
to be longer present, and returned to Norwich, where the whole 
matter was exposed at a public meeting. Notwithstanding the 
manifest injustice of the attempt, and my refusal to have any- 
thing to do with it the moment I discovered its unfairness, these 
wise and clever and very just Newtonians would have the world 
believe that they had once and for ever settled the question of 
the earth’s true form and magnitude. Such tricks are unworthy 
of the cause, and the men who can condescend to deal in them 
can do no real service to the school to which they belong. 
I beg to give the friends of the Newtonian system the following 
simple challenge : To select six miles of still water, place a boat 
at one end, with a flag say six feet above the surface of the 
water. Now, at the other end, let a good telescope be fixed at 
an elevation of eighteen inches ; I affirm that the boat and its 
flag will be distinctly visible ; whereas, if the earth is a globe of 
8,000 miles diameter, the top of the flag would be more than 
seven feet below the intervening arc of water. This is my chal- 
lenge, and let the Newtonians decide that it shall be accepted ; 
saying with me, ‘‘let us stand or fall by the result!” 
1, Hawley Villas, Chalk Farm Road, PARALLAX 
London, July 18 
[We print ‘Parallax’s” letter, but we warm everybody 
against accepting his challenge. Mr. Wallace’s treatment at 
the hands of these gentry shows us what to expect. Let 
“Parallax” take a good telescope and a return ticket to some 
seaside place and watch the ships travelling to and fro over 
the horizon. We offer him space in NaTureE to detail his 
observations, and to explain them, if he can, on any other theory 
than the received one.—ED.] 
Eclipse of the Moon 
Tue eclipse ot Tuesday evening (July 12) exhibited some in- 
teresting variations in tint and degree of illumination in different 
parts or the shadow. There seems to haye been a dark spot, 
perhaps half the moon’s diameter, about the centre of the umbra, 
nearly, if not quite, free from refracted light ; outside this a ruddy 
zone; and beyond this again, to the edge of the shadow, a 
region strongly illuminated, comparatively speaking, with 
yellowish pink, as it appeared when projected upon the entering, 
or yellowish green upon the emerging moon. It is true that 
just after the commencement, and some little time before the 
end of the eclipse, the part just within the shadow appeared 
darker than the eclipsed limb ; but this, I think, must have 
been an optical effect caused by the overpowering light of the 
uneclipsed portion. 
When, however, abcut two-thirds or three-quarters of the 
moon’s surface was covered, both before and after totality, the 
illumination of the umbra near its boundary was very conspicuous. 
The ‘‘seas” reflected less light than the other portions, and the 
regions along the south limb, and between the north limb and 
Mare Imbrium, were specially bright. These gave almost the 
effect of the illuminated cusps of the moon being distorted, and 
prolonged into the shadow. When the eclipse became total, 
the eastern hemisphere, about the region of Oceanus Procellammus, 
was covered by a dark shade, so dark that the extreme eastern 
limb was scarcely if at all visible. A short time after totality 
the moon was quite hidden by clouds, and remained so, except 
ing occasional momentary glimpses, during which nothing could 
be seen, excepting that she was visible as a dull, pinkish light, 
till just before the end of the total phase, when the clouds broke 
away from her neighbourhcod in a marvellously dramatic way. 
The emerging was wonderfully beautiful ; first a strong, greenish 
light appeared along the eastern limb; this changed to silvery 5 
then bright, full yellow. The eclipsed part was moderately 
bright, shining with a reddish light, excepting a deeper shade 
over the western hemisphere. In fact, the appearance was 
exactly analogous to that at the commencement of totality. I 
regretted extremely that I had not the opportunity of watching 
whether the dark spot really traversed the disc from side to side, 
but I have little doubt that at the time of central eclipse the 
moon presented a well-marked annular phase. 
As the gathering of clouds, and their sudden dispersion at the 
end of the total phase, seems a striking instance of the supposed 
influence of moonlight in dissipating vapour, it is perhaps well 
to mention that after the end of the eclipse, clouds appeared to 
be again gathering round the moon. 
The telescope I used was a 34-inch refractor, armed with a 
power of 35. Gro. C. THOMPSON 
Cardiff, July 17 
Wave-lengths of Complementary Colours 
In applying Mr. Maxwell’s observations to the verification of 
a hypothesis (see NATURE for July 7), Mr. Murphy identifies 
complementary colours by their ames, overlooking the fact that 
the observations themselves afford pretty accurate determinations 
of several pairs. Separate results are given for two observers in 
Tables vi, and 1X. of the memoir formerly cited by Mr. Murphy 
(Narurg, April 28), and are laid down graphically in figures 4 
ands. From the latter form of the data, as the more convenient, 
though no doubt the less accurate, the following formula was 
obtained by interpolation, for the relation between complementary 
wave-lengths :— 
(a—L) (L’- a’) = M?; 
where A is a wave-length between 2350 and 21co (in Fraun- 
hofer’s measure) ; A’ is its complementary between 1820 and 
1700; and L, L’, M are quantities differing for different eyes, 
and having the values 
2076 1842 77°9 for observer **K 3?" 
2132°5 1859°4 51°2 for cbserver ‘‘J.” 
Mr, Murphy’s complementaries are not in general really comple- 
mentary for either observer. Independently ofthis, Mr. Murphy’s 
probable error is about °53, that is, over one in 100: the 
probable error of the formula is certainly under one in 500, 
between the limits stated. C. J. Monro 
4 ¢ 
THE APPLICATION Ok PHOTOGRAPHY TO 
MILITARY PURPOSES 
M ODERN warfare may in many respects be considered 
as so many applications of science. Not only is 
war matériel designed and manufactured nowadays upon 
G 
