May 12, 1870} 
passed (northwards) up the east side of the lake. He tells 
the difficulties created by the flooded rivers at its north end ; 
one of these was the Luo, mentioned, as I have else- 
where pointed out, by the Portuguese as five days’ distant 
from the Cazembe. Again, further north Dr. L. had to 
wade through the Chungu near an old_ site of the chiet’s 
town and where Larcerda died. Now, Father Pinto, when 
he left the Cazembe on his way homewards, did not reach 
the Chungu where he disinterred Lacerda’s bones (sub- 
sequently lost in the retreat), till the 3rd day. Thus it is 
quite evident that the north end of Lake Moero is ‘south of the 
Cazembe’s residence. With respect to the course of the Luapula 
northwards, Mr. K. Johnston may frest assured that Dr. L.’s 
statements have not the slightest foundation. The Luapula 
does not take the name of Lualaba, nor does it join the Luviri 
towardsthe north. That the Chambezi falls into the Luapula 
was ascertained ,by Dr. Lacerda 70 years ago, and all that 
Dr. Livingstone has ascertained is that his own views on the 
subject were erroneous. As to the further course of these rivers 
let us take the evidently unbiassed evidence of the Arabs who 
met Dr. Livingstone in the interior of Africa, and a brief account 
of whose travels appeared in the transactions of the Geographical 
Society of Bombay, 1862. From the western shore they 
travelled in 27 days to the broad river Maroongo. ‘This is the 
Luapula, which, by strangers reaching it from the north, is named 
after the Arungo, who dwell on its western side. ‘‘ Roonda 
(Lunda) is on the banks of the Rooapoora, which runs north to 
Tanganyika.” Here the rude observers confound the river which 
does reach the Nyanza, with Lake Mofo. Neither need we be- 
lieve that the place is called Lunda by the natives. But this 
among African traders is a wide-spread name. By the Portuguese 
and their native agents the dominions of the Muata-ya-Nvo and 
of the Cazembe are all called Lunda. ‘‘25 days west (SW) of 
the Cazembe are the copper mines and the town Katanga. ‘The 
river Rafira (Luviri) flows past Katanga, and joins the Rooa- 
poora to the N.” There is much reason for believing that the 
Luviri flows south-eastwards from Kanyika, but perhaps the 
author’s meaning is that the river wheels round to the north. 
Dr. Livingstone saw nothing of Lake Bangweolo. Lake Moero 
he saw only on the east and north, and not connectedly ; most 
of his statements respecting its size, &c., must be due to hearsay. 
The mountains that he speaks of are the hills Chimpire, noted 
in two groups by the Portuguese. It is remarkable that when in 
his missionary travels he met with the name Mpire, a hill, he 
supposed it to be the Sichuana numeral mbili, éwo (hills), a | 
flagrant mistake. The Portuguese reported that the elevated 
country on the way to the Cazembe lies in ridges, with pools of 
water in the successive hollows. They learned that there was 
a great marsh at the confluence of the Chambeze and Luapula. 
Further north they saw numerous swamps and lagoons, and 
heard of more. They were told that to the west lay the great 
lagoon which Caetano Pereira spent a whole day in wading 
through. This was Carucuize, the nucleus of the Moero, The 
pombeiros, or native commercial travellers from Angola to the 
Cazembe, marched down the eastern bank of the Luapula five 
days before they turned eastward to Lake Mofo. That river, 
therefore, does not ordinarily flow through a lake. Dr. Living- 
stone evidently found the country in a state of unusual flood, 
with the fens and lagoons united into great lakes. From the dis- 
trict of the Fumo Moiro, at thenorth-east margin of the flood, he has 
made the name of the lake. As he finds every pool to belong to 
the system of the Nile, it is natural that, in his exalted imagina- 
tion, the hills should rise into mountains. The Alunda, or 
Balunda as he calls them, being originally from the banks of the 
Lualaba, nourish a superstitious regard for that river. While 
the traveller, therefore, thought of nothing but the Nile, his 
native hearers knew of no great rivers but the Lualaba and its 
immediate neighbours, the Luviri and Luburi (in the printed letter 
misread Soburi.) His inquiries pointed to the N. or N.E. ; 
they answered respecting the S.W. They mistook the object of 
his ardent curiosity, and he was only too ready to misinterpret 
their communicativeness. Hence the confusion of rivers, right 
and left, the lakes Ulenge, Chowambe, &c., of which the less 
said at present the better. After such a conclusion it may 
perhaps be consolatory to remark that it would be labour thown 
away to lead all the great rivers of south tropical Africa to the 
river of Gondokoro. Dr. Peney, who studied the character of 
this stream, found that it varied often, but that it never rose in 
flood more than two feet above its mean level. This increase in 
a wide spreading river near the equator barely suffices to com- 
NATURE 
pensate the loss by evaporation. Consequently, the floods at 
Gondokoro have no perceptible effect on the river a few degrees 
lower down. The river of Gondokoro, therefore, contributing 
nothing whatever to the floods of Egypt, must be regarded as a 
very subordinate branch of the Nile. 
Dr. Beke wonders (NATURE, No. 9) why I give the name 
Nyanza to Lake Tanganyika. He here touches upon an im- 
portant subject, interesting in its bearing both on geography and 
on the intrigues of geographical coteries. The assertion that in 
the name Lake Tanganyika there lurks some fraudulence, will of 
course be received with incredulity, and therefore its justification 
will be impossible without some historical development. But if 
encouraged, I am prepared to show that, with respect to the 
lake, the geographical world labours under a delusion designedly 
produced. Wie Daic: 
Apparent Size of the Moon 
My original intention was to put together several vere cause, 
which might be found, concurrently, to contribute to the univer- 
sal impression that the moon’s disc is larger or smaller, accord- 
ing as it is nearer to the horizon, or to the meridian. I shall 
content myself, however, with calling attention to what I am 
now persuaded is the nature of that impression. ‘‘ Sweet are the 
uses of adversity.” An attack of hemiopsia is always serious, and 
may be dangerous (see NATURE, Feb. 24th, 1870; p. 444). I 
think I owe to it the discovery (for such it was to me), that the 
variable standard of angular magaitude which infects our visual 
judgment, can be detected in a small room as certainly as in 
view of the celestial vault. The distressing affection which suc- 
ceeds the hemiopsia, as soon as it forms a broken arch around the 
central hole of the retina, is an instructive spectre in regard to the 
question I am considering. Being referred to two equally distant 
sites on the wall of the room, one horizontal and the other consi- 
derably elevated, the spectre seems larger in the former than in the 
latter. I soon proved that this was no accident case. I extem- 
porised a very rough experiment on this wise—I placed a disc 
141 inches in diameter on the wall 7 feet from the ground, and 
selected a horizon so that the base of the disc and the horizon 
were equidistant from a fixed point of observation. I found the 
disc was about 30° above the horizon. I now took six persons 
successively, and made each person take an observation from 
that point, first looking at the disc, and then transferring it in 
mind to the horizon, where I carefully marked the estimated 
size. The maximum was 133, the minimum 108, and the mean 
12h inches. This result is, of course, equivalent to saying that 
had an equal-sized disc been placed on the horizon, its diameter 
would, taking the average, have appeared to be 1$ inch greater 
than when elevated 30° above it. I think it is worth while 
making this experiment with greater accuracy, and with a greater 
number of persons. I have no doubt Mr. Abbott’s view of the 
case would be fully borne out. But I do not understand why 
the augmentation on the horizon is so much greater in the case 
of the moon and the sun; nor yet why the rising sun does not 
present so striking an augmentation as the rising moon. The 
augmentation of the latter may be partly an effect of external 
conditions ; but the fact of augmentation, in what I have called 
visual judgment, is a question for the physiologist. I should 
much like to know what, for instance, such an authority as 
Helmholtz has to say on the matter. 
The great fault of physicists, me judice, is, and ever was, their 
inability to see more than one side or aspect of a subject. 
Metaphysicians, on the contrary, may see all round it, but do 
not see all sides clearly. Mr. R. A. Proctor (NATURE, March 
3rd, 1870; p. 462) affords me an apt example of the former. 
“<The mind,” he says, “instinctively assigns to the celestial vault 
a somewhat flattened figure, the part overhead seeming nearest 
tous.” That is, taking the angular measure of the moon’s dia- 
meter asa constant quantity, since she seems larger on the hori- 
zon than on the meridian, we must (unconsciously) refer her in 
the former case to a maximum distance. So far so good. But 
the argument is a thesis admitting of an equally valid antithesis. 
The case with me is this, that the moon appears to me to be 
much nearer on the horizon than in any other position! Nor 
am I singular in this. A lady proposed to me as an explanation 
of the apparently augmented size of the horizontal moon, that 
‘probably she is nearer to us there than anywhere else!” Here 
we have the antithesis. We may say, the mind instinctively 
assigns to the celestial vault a somewhat prolate figure, the part 
overhead being furthest from us. That is, assuming (erroneously 
of course) a greater size for the moon’s disc on or near the hori- 
