406 
Icommenced this Address by asking you to follow me in an 
attempt to trace the path which has been followed by a scientific 
idea, in its long and slow progress from the position of a probable 
hypothesis to that of an established law of nature. Our survey 
has not taken us into very attractive regions ; it has lain, chiefly, 
in a land flowing with the abominable, and peopled with mere 
grubs and mouldiness. And it may be imagined with what 
smiles and shrugs, practical and serious contemporaries of Redi 
and of Spallanzani may have commented on the waste of their 
high abilities in toiling at the solution of problems which, though 
curious enough in themselves, could be of no conceivable utility 
to mankind. 
Nevertheless you will have observed that before we had 
travelled very far upon our road there appeared, on the right 
hand and on the left, fields laden with a harvest of golden grain, 
immediately convertible into those things which the most sordidly 
practical of men will admit to have value—viz., money and life. 
The direct loss to France caused by the Pebrine in seventeen 
years cannot be estimated at less than fifty millions sterling; and 
if we add to this what Redi’s idea, in Pasteur’s hands, has done 
for the wine-grower and for the vinegar-maker, and try to capi- 
talise its yalue, we shall find that it will go a long way towards 
repairing the money losses caused by the frightful and calami- 
tous war of this autumn. And as to the equivalent of Redi’s 
thought in life, how can we over-estimate the value of that know- 
ledge of the nature of epidemic and epizootic diseases, and con- 
sequently of the means of checking, or eradicating, them, the 
dawn of which has assuredly commenced ? 
Looking back no further than ten years, it is possible to select 
three (1863, 1864, and 1869) in which the total number of 
deaths from scarlet-fever alone amounted to ninety thousand. 
That is the return of killed, the maimed and disabled being left 
out of sight. Why, it is to be hoped that the list of killed in 
the present bloodiest of all wars will not amount to more than 
this! But the facts which I have placed before you must leave 
the least sanguine without adoubt that the nature and the causes 
of this scourge will, one day, be as well understood as those of 
the Pébrine are now ; and that the long-suffered massacre of our 
innocents will come to an end. 
And thus mankind will have one more admonition that ‘the 
people perish for lack of knowledge ;” and that the alleviation 
of the miseries, and the promotion of the welfare, of men must 
be sought, by those who will not lose their pains, in that dili- 
gent, patient, loving study of all the multitudinous aspects of 
Nature, the results of which constitute exact knowledge, or 
Science. It is the justification and the glory of this great 
meeting that it is gathered together for no other object than 
the advancement of the moiety of science which deals with those 
phenomena of nature which we call physical. May its endeavours 
be crowned with a full measure of success ! 
PROFESSOR H. E. ROSCOE’S OPENING ADDRESS TO 
SECTION B. 
GENTLEMEN,—In the midst of the excitement of the horrible 
war in which the two most scientific nations of the continent are 
now plunged, and in which even the Professors of Chemistry 
and their students take a humane part, let us endeayour to turn 
our thoughts into channels more congenial to the scientific 
inquirer, and allow me to recount to you, as far as I am able, 
the peaceful victories which, since our last meeting in Exeter, 
have been achieved in our special department of chemistry. 
And here may I remind you of the cosmopolitan character of 
science, of the fact that it is mainly to the brotherly intercourse 
of those interested in science, and in its applications to the arts 
and manufactures in different countries, that we must look as the 
small but living fire which in the end will surely serve to melt 
down national animosities, and to render impossible the break- 
ing out of disasters so fatal to the welfare of humanity as that of 
which we are now unfortunately the spectators. 
* With regard to the position of chemical science at the present 
moment, it will not take a careful observer long to see, that in 
spite of the numerous important and brilliant discoveries of 
which every year has to boast, we are really but very imperfectly 
acquainted with the fundamental laws which regulate chemical 
actions, and that our knowledge of the ultimate constitution of 
matter upon which those laws are based is but of the most ele- 
mentary nature. In proof of this, I need only refer to the dif- 
ferent opinions expressed by our leading chemists in a discussion 
whichlately took place at the Chemical Society on the subject of 
NATURE 
[Sez 15, 1870 
the Atomic Theory. The President (Dr. Williamson) delivered 
avery interesting lecture in which the existence of atoms was 
treated as ‘‘ the very life of chemistry.” Dr. Frankland, on the 
other hand, states, that he cannot understand action at a distance 
between matter separated by a vacuous space, and, althongh 
generally granting that the atomic theory explains chemical 
facts, yet he is not to be considered asa blind believer in the 
theory, or as unwilling to renounce it if anything better pre- 
sented itself. Sir B. C. Brodie and Dr. Odling both agree, that 
the science of chemistry neither requires nor proves the atomic 
theory ; whilst the former points out that the true basis of this 
science is to be sought in the investigation of the laws of gaseous 
combination, or the study of the capacity of bodies for heat, 
rather than in committing ourselyes to assertions incapable of 
proof by chemical means. 
Agreeing in the main myself with the opinions of the last 
chemists, and believing that we must well distinguish between 
fact and theory, I would remind you that Dalton’s discovery of 
the Jaws of multiple and reciprocal proportions (I use Dr. Odling’$ 
phraseology), as well as the differences in the power of hydro- 
gen replacement in hydrochloric acid water, ammonia, and 
marsh gas, are facts, whilst the explanation upon the assumption 
of atoms is, as far as chemistry is as yet advanced, a theory. 
If, however, the existence of atoms cannot be froved by chemical 
phenomena, we must remember that the assumption of the atomic 
theory explains chemical facts, as the undulatory theory gives 4 
clear view of the phenomena of light ; thus, for instance, one of the 
most important facts and relations of modern chemistry, which it 
appears difficult if not impossible to explain without the assumption 
of atoms, is that of Isomerism. How otherwise than by a different 
arrangement of the single constituent particles are we to account 
for several distinct substances in which the proportions of carbon, 
hydrogen, and oxygen are the same? Why, for instance, should 
48 parts, by weight, of carbon, 10 of hydrogen, and 16 of oxygen, 
united together, be capable of existing as three different chemical 
substances, unless we presuppose a different statical arrangement 
of the parts by which these differences in the deportment of the 
whole are rendered possible. If, then, it be true that chemistry 
cannot give us positive information as to whether matter is in- 
finitely divisible and therefore continuous, or consists of atoms 
and is discontinuous, we are in some degree assisted in this 
inquiry by deductions from physical phenomena which have been 
recently pointed out by the genius of Sir William Thomson. Hé 
argues from four different classes of physical phenomena, and 
comes to the conclusion not only that matter is discontinuous, 
and therefore that atoms and molecules do exist, but he éven 
attempts to form an idea of the size of these molecules, and he 
states that in any ordinary liquid, transparent or seemingly opaque 
solid, the mean distance between the centres of contiguous mole- 
cules is less than the 100 millionth, and greater than the 2,000 
millionth of a centimetre. Or, to, form a conception of this 
coarse-grainedness, imagine a raindrop, or globe of glass as latge 
as a pea, to be magnified up to the size of the earth, each con- 
stituent molecule being magnified in the same proportion, the 
magnified structure would be coarser grained than a heap of small 
shot, but probably less coarse grained than a heap of cricket 
balls. There is, however, another class of physical considera= 
tions which renders the existence of indivisible particles more than 
likely. Lrefer to the mechanical theory of gases, by means of 
which, thanks to the labours cf eminent English and Getman 
philosophers, all the physical properties of gases—their equal 
expansion by heat, the laws of diffusion, the laws of alteration of 
volume under pressure—can be shown to follow from the simple 
laws of mechanical motion. This theory, however, presupposes 
the existence of molecules, and in this direction, again, we fiiid 
confirmation of the real existence of Dalton’s atoms. Tndeéd; 
it has been proved that the average velocity with which the 
particles of oxygen, nitrogen, or common air are continually pré- 
jected forwards amounts, at the ordinary atmospheric pressure, 
to 50,000 centimetres per second, whilst the average number of 
impacts of each of these molecules is 5,000 million per second, ° 
The mention of the molecular motions of gases will recall to 
the minds of all present the great loss which English sciencé hag 
this year sustained in the death of the discoverer of the laws of 
gaseous diffusion. Throughout his life Graham’s aimt was the 
advancement of our knowledge in the special subject of the 
molecular properties of gases. With this intent he unceasingly 
laboured up to the moment of his death, in spite of failing health 
and pressure of official business, unfolding for posterity some. of 
the most difficult as well as the most interesting secrets of nature 
in this branch of our science. ‘‘ What do you think,” he writes 
