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Oct. 6, 1870] 
NATURE 
403 
passed unnoticed at the time. Upon consulting the three works 
for elucidating the history of any given object, such results as 
these are frequently obtained. An object is found in Schréter 
designated by a Greek or other character, sand its appearance 
described in his text. This object may be altogether omitted 
by Lohrmann, but given on Beer and Madler’s map, and objects 
are by no means rare which may be found on Lohrmann, but 
omitted by Beer and Madler, and wice versa. 
Were the results of the labours of Julius Schmidt during a 
period of nearly thirty years given to the public, there can be no 
doubt that our knowledge of selenography would be greatly ad- 
vanced. His chart must contain a large proportion of the objects 
previcusly recorded by Schréter, “ohrmann, and Beer and 
Madler ; and judging from the instances already alluded to, of 
apparent omissions by one or other of the above-named observers, 
it is highly probable that the number of such instances would be 
much mnereased. The value of his measures (4,000) of the alti- 
tudes of lunar mountains for comparison with or addition to those 
of Schroter and Madler, cannot admit ofa doubt. His published 
catalogue of rills is very valuable in this respect. It is to Schmidt 
that we are indebted for one of the most important announce- 
ments bearing on the subject of lunar activity, that of a change 
in the crater Zinné, ‘‘ which,” says Madler (Reports British 
Association, 1868, p. 517) “ has hitherto offered the only authentic 
example of an admitted change.” He had previously said (same 
report): “‘ What has lately been observed in the crater Linné 
proves, at all events, that ¢/eve real changes haye taken place, 
and that, too, under circumstances even visible to us.”” Further 
on, however, the great selenographer remarks that on the 10th of 
May, 1£67, his eye having undergone an operation for cataract, 
he attempted an observation of Z/mnéin the heliometer of the 
Observatory at Bonn, and found it shaped exactly, and with the 
same throw of shadow as he remembered to have seen it in 1831. 
“« The event,” he says, “of whatever nature it might have been, 
must have passed away without leaving any trace obse. vable 
by me.” Thedoubt still hanging over this object is well 
known, and it may be regarded as furnishing, at least, one 
of the instances of the present state of the question of activity. 
The uncertainty attaching to the question of change in this 
particular insiance mainly arises from the difficulty of de- 
ciding upon the accuracy or otherwise of the delineations 
of Lohrmann and Beer and Madler, although both describe 
it as showing a diameter of five or six English miles. Gene- 
rally speaking, the observations between October 1866 and 
‘July 1870, all agree in its present appearance, differing 
greatly from that which it must have presented according to the 
delineations and descriptions of the two selenographers just 
named, also that no change of a physical character has taken 
place in it during the 3 years it has been under observation. 
It has been supposed that photography would solve all such 
- difficulties, and that photograms of the lunar surface taken 
under similar angles of illumination and visual ray would agree 
with each other; but here again precisely the same difficulties 
present themselves which perplexed Schréter, and which have 
been met with in comparing Lohrmann’s and Beer and Madler’s 
works. Objects figured by the earlier selenographers occur on 
some photograms, but not on others, of about the same phase of 
illumination, ‘There appears to be an agency capable of affect- 
ing the visibility of objects, rendering them indistinct or invi- 
sible on some occasions ; while, on others, they are distinctly 
seen on the photograms. Whatever operations may have taken 
place in the crater Zinmné, producing phenomena the recurrence 
of which is vare, in all the examples above mentioned, from 
Schroter’s time to the present, we have phenomena of a different 
character, exceedingly difficult of explanation, and constituting 
an important element in the solution of the question of present 
activity or quiescence ; for unless it be fully proved that a// these 
instances depend upon changes of visual and illuminating angles, 
a strong suspicion will exist of their being more immediately 
connected with the moon itself. To effect such a proof, how- 
ever, is a matter of no small difficulty. Madler alludes to the 
performance of calculations of the most varied kind as necessary 
for the delineation of lunar forms, and in the case before us the 
calculation of several elements for cach separate observation, and 
they are very numerous, is absolutely essential for the purpose 
of referring the phenomena observed to changes cf illumination 
and visual ray. Calculations of this kind have not been made 
to any great extent, and the consequence is, that the entire 
question remains involved in doubt. During the last seventeen 
months, as many as 1,227 observations of the spots on /%ato 
alone have been made, and although the varying state of the 
earth’s atmosphere affects in no slight degree the visibility of 
such delicate objects, phenomena are presenting themselves 
which call for a much more rigorous treatment than has yet 
been accorded to them. The affirmation of change on, or 
quiescence of, the moon’s surface, must depend, not upon the ac- 
cumulation of desultory and undiscussed observations, but upon 
such as are undertaken on a well-arranged system, and discussed 
with reference to every known agency capable of affecting 
them. The present state of the question is therefore one of 
doubt, one that calls for observation of the most vigorous charac- 
ter, ana discussion of the most rigorous nature to settle it. 
Observation of late has been tending towards a registration of 
minute detail detected on the moon’s surface, but discussion in 
various ways is behind the requirements of selenography, and 
until it can keep pace with observation the doubt alluded to 
above must remain. 
SecTion B.—CHEMICAL SCIENCE 
On Artificial Alizarine.—Mr. W. H. Perkin, F.R.S. In in- 
trodacmg Mr. Perkin the President said that that gentleman 
might be regarded as the representative in England of artificial 
colouring matters, and that the subject to be treated of was one 
of great importance, both theoretically and in its practical 
aspects. The author referred to the use of madder and its pre- 
paration called garancine, in the production of Turkey red dye, 
and then traced the history of the investigations ef chemist 
regarding the chemical nature of the colouring matters contained 
in madder-root. About thirty-nine years ago those investigations 
commenced, and ever since that time they have been con- 
tinued by many emment chemists, among others by Graebe, 
Liebermann, Schunck, Strecker, Laurent, Anderson, and others, 
as also those of the author himself. Two colouring compounds 
had been obtained from madder known as alizarine and purpu- 
rine. The exact composition of alizarine had been the subject of 
much discussion among chemists. From that compound a hydro- 
carbon derivative had been obtained which is called anthracene, 
and then from anthracene, as an ingredient of coal-tar and 
mineral pitch, alizarine had been produced by the action of 
various chemical agents. Alizarine, thus artificially produced, 
yields with mordants the same colours on cotton goods as the 
natural alizarine from madder-root. Mr. Perkin performed a 
great yariety of experiments in order to @emonstrate the chemical 
identity of the artificial and natural alizavrine when absolutely 
pure. He had also, during upwards of twelve months, been 
engaged in studying the properties of anthracene and its com- 
pounds, all of which are very markedly fluorescent. There were 
many difficulties in the way of obtaining artificial alizarine in 
large quantities, but they were gradually disappearing. In the 
discussion which followed, Dr. Schunck, F.R.S., referred to the 
alleged differences between the natural and the artificial alizrine, 
and said he had no doubt whatever that the two were identical, 
and he thought the confusion had arisen from persons examining 
impure products. The artificial product was generally supplied 
impure, but the impurities could be separated. He was quite 
satished as to the importance of alizarine, and that it was the only 
essential dye product of madder. Sore years ago he had shown 
that the finest madder pinks contained nothing but alizayine. 
Srecrion C.—GEOLOGY 
On the Extension of the Coal-fields beneath the newer Formations 
of England.—Mr. Edward Hull. Having referred to the paper by 
Sir R. I. Murchison, on the parts of England and Wales in which 
coal may or may not be looked for, the author expressed his 
gratification that his own views coincided in the main with those 
of his chief, especially as regarded the absence of coal in the 
eastern and portions of the midland counties, now everspread by 
mesozoic formations. ‘The author showed that there was evidence 
for believing that the coal measures were originally deposited in 
two continuous sheets, one to the north, and the other to the 
south of a ridge of old land formed of Silurian rocks which 
stretched eastward from Shropshire to the south of the Dudley 
coal-feld. This ridge, or barrier, had never been altogether sub- 
merged beneath the waters in which the coal measures were de- 
posited. Towards the north, the boundaries of the coal formas 
tion were formed by the Cambro-Silurian rocks of North Wales, 
the Lake District, and portions of the southern uplands of Scot- 
land. Over the region north of the barrier, the coal measures 
