Dec. 29, 1881] 
which enable me to invite any person who may wish to make 
themselves acquainted with the modus operandi by actual inspec- 
tion, to come and witness the same. The only formality I 
would impose is the communication of the visitor's card and 
address, and a few hours’ notice, in case the intended visit should 
promise to be inopportune. To reduce the likelihood of this I 
would intimate that the regular observations are made (in the 
present case) within about half an hour before and after the 
hours of six and twelve, morning, noon, evening, and midnight, 
during which the attention of the observer may be understood to 
be entirely preoccupied. At any other hour of the day or night, 
either I or my assistant will be desirous of explaining to the best 
of our ability whatever may be needful. 
My reasons for making this offer so publicly are, in the first 
place, entirely scientific. I wish to give those who are curious 
on the subject a fair opportunity, and I hope to derive informa- 
tion or suggestions from those whose attention is for the time 
engaged in comprehending the details by means of which the 
general result is sought to be obtained. Beyond this, I am also 
desirous of obtaining some indications as to the degree of interest 
actually existing in England on the subject of gravity-measures 
of this kind. 
The present site has a peculiar interest. It is a cellar which 
I have been lucky enough to find very near the desired spot— 
which is that which was occupied in the early part of this cen- 
tury by Kater, Sabine, Foster, and others ; but was afterwards 
necessarily abandoned on the decease of Mr. Browne, of Port- 
land Place, whose house was the vexdezvous of those observers. 
It was in consequence of this abandonment that the intention 
was formed of founding a more permanent central point of 
reference ; and as the establishment of a magnetical observatory 
at Richmond was at that time under consideration, the transfer 
of what may be called the English home of pendulum investiga- 
tions from Portland and Tavistock Places to the new Richmond 
(or ** Kew”) Observatory was decided upon, and accordingly 
when next pendulum experiments were instituted, their site was 
in the Richmond Observatory. It is only recently, however, 
that the necessity of ascertaining the physical relation between 
the two sites has become a practical one. 
Something of the same sort had been experienced in the 
earlier days, when, partly owing to Greenwich Observatory 
having formed the base or fozn¢t @’appui on English soil, of one 
or two foreign series of operations; partly because of the 
obvious anomaly of having the principal English pendulum sta- 
tion in a private house ; special observations were instituted for 
determining the relation of that site to the Greenwich one. 
Greenwich was thus incorporated on the one hand with those 
series which depended on the Portland Place site, while the 
latter was connected with those dependent (if one may use the 
term where all are mutually dependent) on the Greenwich site. 
They were all, in fact, to a certain extent linked together. 
This should explain why re-observation at Greenwich, in con- 
nection with re-observation at Kew, seems likely to meet the 
present want best if supplemented by re-observation also at, or 
very near, the old Portland Place site. I have made the requisite 
observations (subject to some doubt) at Kew, 7.2. at the Rich- 
mond Observatory, and at Greenwich Observatory, and I am 
now doing the same in the cellar above referred to, as represent- 
ing Portland Place. Its exact situation is immediately in rear 
of All Souls’ Church, Langham Place. 
The Kew (or Richmond) Observatory is not a very convenient 
place for observations of this nature. They require attendance 
at all hours, whereas the observatory is situated so far from the 
inhabited part of Richmond as to permit of such attendance 
only at great personal inconvenience.! Also, though a precise 
knowledge of time is of the first importance, the absence of tele- 
graphic communication with Greenwich Observatory and the 
distance from the nearest telegraph station combine at Kew to 
make one dependent on local transits. This is of itself a very 
Serious objection. If to this we add that the pendulum-room at 
the Kew Observatory is too small to allow of the introduction 
of any portable stand or framework such as must of necessity 
be used on voyages—the very restricted space being permanently 
occupied by a fixed support, which does not admit of the same 
dispositions as would be made elsewhere for convenient observa- 
tions, it remains a serious question whether Kew ought to con- 
tinue to be regarded as the fundamental English pendulum 
station, There can be very little doubt, having regard to the 
t T estimate that I walked fully 200 miles to and from my work, in all 
weathers and at all hours, while carrying on the observations at Kew in 
September and October last. 
NATURE 
197 
paramount importance of “me in pendulum experiments, tha+ 
the fundamental station should have a perfect command of tha+ 
element, such as can rarely be obtained except at a fixed astro. 
nomical observatory. 
At the Langham Cellar, after due consideration, I have con- 
cluded to rely on Greenwich alone for time ; sending a chrono- 
meter for the purpose every day. So far, the plan seems to be 
quite satisfactory, being more reliable than noting a transmitted 
signal at the nearest post-office. 
Although I do not think I have touched on any point in this 
letter which is not closely connected with its primary object, I 
must nevertheless apologise for its length. In conclusion I have 
now only to repeat the offer with which I commenced it, that 
any one interested in, or desirous of becoming practically ac- 
quainted with pendulum swinging of this particular kind, may, 
at any time within the next fortnight, visit and inspect the appa- 
ratus in action, by communicating with me, at the address here 
given. J. HERSCHEL 
1, Langham Street, Portland Place, W., December 28 
Dante and the Southern Cross 
«« . . vidi quattro stelle 
Non viste mai, fuor ch’alla prima gente.’” 
Purg. i. 23- 
No one will accuse me of excessive patriotism when I say that 
Dante was one of the very few chosen spirits of the fourteenth 
century who were thoroughly acquainted with all natural pheno- 
mena, so far as they were then known and understood, whilst 
he was perhaps the only one who manifested a decided con- 
tempt for all the pretensions of astrologists and necromancers 
(Inf. xx.). The words of such a man are deserving of the best 
consideration, alike of literary and scientific men ; it is therefore 
to be hoped that before the discussion ends those best qualified 
to speak will throw more light on the lines in question. 
As yet in answer to the query which appearcd in NATURE 
(vol. xxv. p. 152), we have only had a quotation of a well- 
known passage from Humboldt’s ‘‘Cosmos,” and the suggestion 
that Dante must have derived his knowledge of the Southern 
Cross—evidently indicated in the lines at the head of this note 
—from Arabian Globes—a suggestion which, by the way, is ex- 
pressed, or clearly implied, in the ‘‘ Cosmos,” within a page 
from the passage quoted. As to the remark with which both Mr. 
Walker and Mr. Wilks end their notes (NATURE, vol. xxv. p. 
173) that ‘* prima gente” does not refer to Adam and Eve, but to 
the early races which inhabited Europe and Asia, though not 
new, it is obviously correct to the mind of those who know 
how great was the cosmographic knowledge of Dante. Yet, as 
Count de St. Robert states in an ably-written pamphlet on the 
point in question (Torino, 1866), strange to say, Humboldt (who 
has so unhesitatingly stated the opinion of Dr. Galle that in 52° 
30 north latitude in consequence of the precession of the equi- 
noxes, the Southern Cross might have previously reached more 
than 10°, and that it began to become invisible in that latitude 
2900 years before Christ), believed that ‘‘ prima gente” referred 
to our first parents. 
Now, whilst admitting as possible that Dante obtained his 
knowledge of the stars which form the Southern Cross from the 
catalogue of Ptolemy (Almagest, Book vii.), on reading the 
passage, in which occur the two lines quoted above, especially 
in the original, one is irresistibly brought to think that Dante’s 
enthusiastic description of the ‘‘quattro stelle” was inspired 
by the vivid description of a Christian witness of the glorious 
spectacle. The person most likely to have imparted such know- 
ledge to the great poet was Marco Polo, ‘That celebrated 
Venetian traveller returned from his last voyage in 1295, and 
lived in his native town till 1324 (Col. Yule, ‘‘ The Book of 
Ser Marco Polo”). Dante did not visit Venice till 1320, after 
he had finished his ‘‘ Divina Commedia,” but there are many 
reasons for the belief that the two great men met or corresponded 
together. 
With regard to the lines :— 
«. . . quelle tre facelle, 
Di che ’I polo di qua tutto quanto arde.” 
Purg. viii. 89. 
which Dante says were high when the “‘ quattro stelle” were low, 
it is difficult to agree with any of the commentators, because 
neither the Magellanic clouds, nor Achernar, nor any three 
prominent southern stars, correspond satisfactorily to the ‘‘tre 
facelle” alluded to. It must not be forgotten that accurate 
