Dec. 28, 1882] 
NATORE 
203 
rocks of much coarser grain than the modern ones. But 
I am not aware that this is the case. Again, to understand 
such blasts, the earliest trees should have trunks of 
enormous thickness and their leaves must have been very 
tough, or they would have been torn to shreds. There 
seems to be no reason to suppose that the trees of the 
Carboniferous period present marked peculiarities in 
these respects.” 
“Tt is on these grounds that I venture to dissent from 
Mr. Ball in the geological interpretation to be placed on 
the tidal theory, and I think we must put these violent 
phenomena in pre-geological periods.” 
But is it necessarily true that the prodigious tides must 
have produced a coarser material as the result of their 
grinding than is found in the later rocks? I can imagine 
it to be contended that the more powerful mill would 
produce the finer flour, but in truth I really do not 
see that we have any a@ f7iv7z grounds for deciding 
whether the déJris produced by mighty tides should 
be fine or coarse. Have we not illustrious authority 
for invoking our “Domestic Productions’’ to throw 
light on obscure questions removed from actual obser- 
vation. Let us look at the biggest tides we know 
of, and see whether they are associated with fine 
mud or with coarse. I appeal to every one who has 
stood on the Clifton Suspension Bridge or walked on the 
Beach at Weston-super-Mare to answer this question. In 
both cases they will see mud of a fineness and a stickiness 
that is proverbial; yet that mud is washed twice every 
day by the mightiest tides in the British Islands, I 
do not say, nor do I believe, that the fineness of the mud 
in the Avon is the consequence of the great tides; but 
I think the illustration is a fair reply to an argument 
which says the tides in ancient days cannot have been of 
great size, because the mud with which those tides are 
associated is not coarse. 
In the second place, Mr. Darwin urges against me the 
trees of the Carboniferous epoch, and his inference that 
the tremendous tides cannot have existed in the Carboni- 
ferous epoch is probably well founded. But I have not 
said that these tides did exist in the Carboniferous epoch. 
I can only again repeat that my argument supposed that 
the mighty tides may have existed in the times when the 
very earliest stratified rocks were deposited. In the 
course of ages, as the moon receded, so the tides 
gradually dwindled down until in the comparatively 
modern time indicated by the Carboniferous epoch, they 
may have been small enough to be connected with the 
wonderful coal vezetation. 
I had, as I was bound to do, most carefully weighed 
the words in which I addressed you from this place last 
year. Iwas aware that the opinion I advanced would 
meet with opposition. This was a reason why I should 
consider the subject most carefully before I spoke, 
but it was not a reason why I should withhold the 
views at which I had arrived. I have again considered 
the matter with the results now set forth, and I have 
seen no reason to depait in the slightest degree from 
the position which I had previously adopted. 
MARS* 
HE similarity which has long been thought to exist 
between our own globe and the planet Mars would 
naturally commend itself to careful examination at the 
hands of such observers as possess instruments adequate 
to the inquiry. The shadowing of large portions of its 
surface with patches which easily lend themselves to the 
supposition of being collections of water, the occasional 
indistinctness of their outlines, so strongly indicative of 
* ** Areographische Beitrage zur genauern Kenntniss und Beurtheilung des 
Planeten Mars.” Von Dr. J. H. Schroeter: herausgegeben von H.G van 
de Sande Bakhuyzen, Director der Leidener Sternwarte. 8vo, 447 pp., with 
Atlas. Leiden: E. J. Brill 
atmospheric obscuration, the clothing of either pole with 
the semblance of a snowy mantle obedient in its extent to 
solar action, all this would bespeak of itself a critical 
investigation. And the challenge has been taken up from 
an early period, and to an extent which would probably 
surprise those who are unfamiliar with the subject. Al- 
ready in 1873 the number of drawings collected by Dr. 
‘Yerby of Louvain, than whom no man is more intimately 
conversant with areography, amounted to 1092, and the 
nine subsequent years, which have included among others 
the celebrated representations of Green and Schiaparelli, 
have greatly augmented that imposing number. We 
should be mistaken, however, if we were to estimate the 
progress of our knowledge by the multiplication of de- 
signs. In this case the ancient saying mAéov fir mavrds 
would probably express too large a proportion. The 
increase, if in some respects not to be regretted, brings 
with it additional elements of uncertainty, if not of error. 
Many representations might be discarded with positive 
advantage to the final conclusion : like numerical observa- 
tions whose unworthiness is detected by their wide devia- 
tion from the mean of the rest, the result is all the surer 
for their exclusion. An unpleasant experience proves 
that the most careful observer is not always the most 
successful draughtsman, nor in such matters is zeal any 
pledge of excellence. Comparison of the results obtained 
by different astronomers leads to the conclusion that, 
after due allowance has been made for instrumental and 
atmospheric differences, all men do not see alike, or 
interpret in the same way what they see, or transfer the 
image to paper with equal success. Here it is that photo- 
graphy, though not exempt from defects and hindrances 
of its own, is now beginning to render invaluable aid. 
But such an object as the disc of Mars would not lend 
itself very readily at present to the camera, and the pencil 
and the brush must do the best they can till some further 
advance is made to supersede them. 
But bowever improved may be our future representa- 
tions, and whatever may be the result—on every supposi- 
tion most interesting—of the keen scrutiny that is in store 
for the next opposition of the planet, it would undoubtedly 
be an injudicious course to discard as unworthy of study 
and comparison the delineations of earlier days. Less 
valuable, if standing alone, they may attain considerable 
importance in the elucidation of some otherwise unex- 
plained difficulty ; and evidence which, unsupported, 
might be of little weight, may acquire especial conse- 
quence from its collateral bearing on more direct testi- 
mony. The comparatively rude and defective sketches of 
a long-passed era, contained in the publication before us, 
executed in a spirit of unwearied industry and unimpeach- 
able fidelity, but under the influence of a mistaken 
impression, form a striking illustration of the previous 
remarks. 
The history of the “ Areographische Beitrage” is con- 
nected with a very lamentable occurrence in the life of 
the worthy old Hanoverian observer, Dr. Johann Hier- 
onymus Schréter. He had long been settled in a Govern- 
ment office at Lilienthal, not far from Bremen, where his 
almost innumerable observations on sun, moon, and 
planets (with stars he did little) had been carried on with 
reflectors of various sizes—two by Sir W. Herschel of 
4 and 7 feet focal length, others by Schrader, of Kiel, of 
7, 11,15, and 27 (26 English) feet, and a 4 inch object- 
glass by Dollond, equatorially mounted. His passion 
fer observation would never have allowed so interesting 
an object as Mars to escape him, and accordingly we 
find that between the years 1785 and 1803 he had accu- 
mulated 217 designs, with a corresponding description 
marked by all the minute preciseness of detail and in- 
ference which characterise his other labours. The work 
had been promised for publication at Easter, 1812, but 
had been somehow delayed, when an event occurred on 
the night of April 20, 1813, in connection with the occu- 
