SCIENCE. 
173 
was the origin of the earliest mountain chains. I make no 
objection to the hypothesis, which, to say the least, seems 
to be the best that can be offered, and looks highly proba- 
ble. But, assuming that it is true, these hypothetical events 
took place so long before authentic geological history be- 
gan, as written in the rocks, that the earliest of the physical 
events to which I have drawn your attention in this address 
was, to all human apprehension of time, so enormously re- 
moved from these early assumed cosmical phenomena, that 
they appear to me to have been of comparatively quite 
modern occurrence, and to indicate that from the Lauren- 
tian epoch down to the present day, all the physical events 
in the history' of the earth have varied neither in kind nor 
in intensity from those of which we now have experience. 
Perhaps many of our British geologists hold similar opin- 
ions, but if it be so, it may not be altogether useless to have 
considered the various subjects separately on which I de- 
pend to prove the point I had in view.” 
MATHEMATICS AND PHYSICS. 
The address was delivered by the president, Prof. W. 
Grylls Adams. In it he dealt with the subject of mag- 
netic disturbances, and pointed out that in many instances 
the disturbances at the various stations of observations 
were not precisely alike, showing probably the change of 
the direction or intensity of the earth’s magnetism arising 
from the solar action upon it. He believed there was a 
sufficient cause for all our terrestrial magnetic changes, for 
these masses of metal were ever boiling up from the lower 
and hotter levels of the sun’s atmosphere to the cooler up- 
per regions, where they must again form clouds to throw 
out their light and heat, and to absorb the light and heat 
coming from the hotter lower regions ; then they became 
condensed and were drawn again back towards the body of 
the sun, so forming those remarkable dark spaces or sun- 
spots by their down-rush towards the lower levels. In these 
vast changes, which we know from the science of energy' 
must be taking place, but of the vastness of which we can 
have no conception, we have abundant cause for the mag- 
netic changes which we observe at the same instant at dis- 
tant points on the surface of the earth, and the same cause 
acting by induction on the magnetic matter within and on 
the earth may well produce changes in the direction of its 
total magnetic force, and alter the direction of its magnetic 
axis. These magnetic changes on the earth will influence 
the declination needles at different places, and will cause 
them to be deflected. The direction of the deflection must 
depend on the situation of the earth’s magnetic axis, or the 
direction of its motion with regard to the stations where the 
observations are made. Thus, both directly and indirectly', 
we find in the sun not only' the cause of diurnal magnetic 
variations, but also the cause of these remarkable magnetic 
changes and disturbances over the surface of the earth. 
CHEMISTRY. 
The address was delivered by the president, Dr. J. H. 
Gilbert, F.R.S., who referred mainly to the subject of 
agricultural chemistry', and in the course of his remarks 
said, referring to the assimilation of carbon, that the whole 
tendency' of observations was to conform to the opinion 
put forward by De Saussure about the commencement of 
the century, and so forcibly insisted upon by Liebig, forty 
years later, that the greater part, if not the whole, of the 
carbon, was derived from the carbonic acid of the atmo- 
sphere. Judging from more recent researches, it would 
seem probable that the estimate of one part of carbon or 
carbonic acid in 10,000 of air was more probably too high 
than too low as an estimate of the average quantity in the 
atmosphere of our globe. Large as was the annual accu- 
mulation of carbon from the atmosphere over a given area, 
it was obvious that the quantity must vary' exceedingly with 
the variation of climatical conditions. It was, in fact, sev- 
eral times as great in the case of the tropical vegetation — 
that of the sugar-cane, for instance. And not only was the 
greater part of the assimilation accomplished within a com- 
paratively small portion of the year, but the action was lim- 
ited to the hours of daylight, whilst during darkness there 
was rather loss than gain. In a general sense it might be 
said that the success of the cultivator might be measured by 
the amount of carbon he succeeded in accumulating in his 
crops. And as the amount of carbon accumulated de- 
pended on the supply of nitrogen in an available form 
within the reach of plants, it was obvious that the question 
of the sources of the nitrogen of vegetation was one of first 
importance. The result of experiments that had been con- 
ducted went to prove — first, that without nitrogenous ma- 
nure, the gramineous crops annually ydelded, for many 
years in succession, much more nitrogen over a given area 
than was accounted for by the amount of combined nitro- 
gen annually coming down in the measured aqueous de- 
posits from the atmosphere; second, the roots yielded more 
nitrogen than the cereal crops, and the leguminous crops 
much more still; and third, that in all cases — whether of 
cereal crops, root crops, leguminous crops, or a rotation of 
crops — the decline in the annual yield of nitrogen, when 
one was supplied, was very great. The next point referred 
to was the condition of the nitrogen in our various crops. 
They' could not say that the whole of the nitrogen in the 
seeds with which they' had to deal existed as albuminoids. 
But they -might safely assume that the nearer they ap- 
proached to perfect ripeness, the less of non-albuminoid 
nitrogenous matters would they' contain; and in the case of 
the cereal grains, at any rate, it was possible that if really 
perfectly ripe, they' would contain very nearly the whole of 
their nitrogen as albuminoids. 
GEOLOGY. 
The address was delivered by the President, H. C. 
Sorly, LL.D., F.R.S., who took for his subject the com- 
parative structure of artificial slags and eruptive rocks. 
His conclusions may be thus summed up : 
The objects I have described may be conveniently separ- 
ated into three well-marked groups, viz. : artificial slags, 
volcanic rocks and granite rocks. My own specimens all 
show perfectly well-marked and characteristic structures 
though they are connected, in some cases, by intermediate 
varieties. Possibly, such connecting links might be more 
pronounced in other specimens that have not come under 
my notice. In any case, the facts seem abundantly suffi- 
cient to prove that there must be some active cause for such 
a common, if not general, difference in the structural char- 
acter of these three different types. The supposition is so 
simple and attractive, that I feel very much tempted to sug- 
gest that this difference is due to the presence or absence of 
water as a gas or as a liquid. In the case of slags it is not 
present in any form. Considering how large an amount of 
steam is given off from erupted lavas, and that, as a rule, 
no fluid cavities occur in the constituent minerals, it ap- 
pears to me very plausible to suppose that those structures 
which are specially characteristic of volcanic rocks are, in 
great measure, if not entirely, due to the presence of asso- 
ciated or dissolved vapor. The fluid cavities prove that 
water was sometimes, if not always, present as a liquid dur- 
ing the consolidation of granitic rocks, and we can scarcely 
hesitate to conclude that it must have had very consid- 
erable influence on the rock during consolidation. Still, 
though these three extreme types appear to be thus 
characterized by the absence of water, or by its pres- 
ence in a state of vapor or liquid, I think we are 
scarcely in a position to say that this difference in the 
conditions is more than a plausible explanation of the 
differences in their structure. Confining our atten- 
tion to the more important crystalline constituents 
which are common to the different types, we may say that 
that the chief structural characters of the crystals are as 
follows . (a) Skeleton crystals, (b) Fan-shaped groups, (c) 
Glass cavities, (d) Simple crystals, (c) Fluid cavities. These 
different structural characters are found combined in differ- 
ent ways in the different natural and artificial products, and 
for simplicity I will refer to them by means of the affixed 
letters. The type of the artificial products of fusion mav 
generally be expressed by a 4- b or b + c ; that is to say, ft 
is characterized by skeleton crystals and fan-shaped groups, 
or by fan-shaped groups and glass cavities. In like man- 
ner the volcanic group may be expressed occasionally by 
b + c, but generally by c + d, and the granitic by d + c 
These relations will be more apparent if given in the form 
of a table as follows : 
Slag type 
Volcanic type. . 
Granitic type . . 
j a + b 
( b + c 
j b + c 
' t c + d 
d + e 
