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 yielded, 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 musl have had very consid- 

 erable influence on the rock duiing 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, (e) Fluid cavities. These 

 difierent 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 + b or b + c ; that is to say, it 

 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 (/ + e 

 These relations will be more apparent if given in the form 

 of a table as follows : 



ci \ a + b 



Slag type.. 



Volcanic type. . 

 Granitic type . . 



( 



\ 



b + c 



d 



d + e 



