SCIENCE. 
1 8 1 
tially decomposed by oxalic acid till the color is reduced to 
a bluish-black tinge. 
Application . — A suitable quantity of the re-agent, pre- 
pared as above, is added to a solution of free ammonia or 
its carbonate, in the same way that Nessler’s solution of 
mercuric per-iodide is used in Manklyn’s well-known pro- 
cess. 
Result . — The combination of the ammonia with part or 
all of the oxalic acid of the colorless ferric oxalate of the 
re-agent, and the blackening of the solution by the re-form- 
ation of ferric gallate. 
Estimation of Ammonia . — By an imitation of a standard 
solution of ammonia with the re-agent, as in Wanklyn’s 
mode of Nesslerizing. When the solution to be tested 
and the imitation solution correspond in color, it is 
inferred that they contain equal quantities of ammonia. 
In this process the standard ammonia test should be made 
from the carbonate , and its strength may be such that one 
litre shall contain one milligramme of ammonia, or one 
part in a million. Another and more direct way of esti- 
mating ammonia is by adding a standard test solution of 
oxalic acid to the blackened solution of the re-agent and 
liquid to be tested, till the original color is produced, and 
from the known quantity of oxalic acid used to calculate 
the quantity of ammonia in the resulting oxalate. Chem- 
ists will find this re-agent both convenient and sensitive. 
THE UNITY OF NATURE. 
By the Duke of Argyll. 
In the preface to the first edition of the “ Reign of Law,” 
published in 1866, the following passage occurs : — “ I had 
intended to conclude with a chapter on Law in Christian 
Theology. It was natural to reserve for that chapter all 
direct reference to some of the most fundamental facts of 
Human Nature. Yet, without such reference, the ‘ Reign 
of Law,’ especially in the ‘ Realm of Mind,’ cannot even 
be approached in some of its very highest and most impor- 
tant aspects. For the present, however, I have shrunk 
from entering upon questions so profound, and of such 
critical import, and so inseparably connected with religious 
controversy.” 
The great subject spoken of in this passage has ever 
since been present with me. Time, indeed, has only in- 
creased my sense of its importance. But the years have 
also added, perhaps in more than equal proportion, to my 
sense of its depth and of its difficulty. What has to be 
done, in the first place, is to establish some method of in- 
quiry, and to find some secure avenue of approach. Before 
dealing with any part of the Theology which is peculiarly 
Christian, we must trace the connection between the Reign 
of Law and the ideas which are fundamental to all religions. 
It is to this preliminary work that the following chapters 
have been devoted. Modern Doubt has called in question 
not only the whole subject of inquiry, but the whole fac- 
ulties by which it can be pursued. Until these have been 
tested and examined by some standard which is elemen- 
tary and acknowledged, we cannot even begin the work. 
It has appeared to me that not a few of the problems 
which lie deepest in that inquiry, and which perplex us 
most, are soluble in the light of the Unity of Nature. Or 
if these problems are not entirely soluble in this light, at 
least they are broken up by it, and are reduced to fewer and 
simpler elements. The following chapters are an attempt 
to follow this conception along a few of the innumerable 
paths which it opens up, and which radiate from it through 
all the phenomena of the Universe, as from an exhaust- 
less centre of energy and of suggestion. 
It is the great advantage of these paths that they are al- 
most infinite in number and equally various in direction, 
To those who walk in them nothing can ever come amiss. 
Every subject of interest, every object of wonder, every 
thought of mystery, every obscure analogy, every strange 
intimation of likeness in the midst of difference — the whole 
external and the whole internal world — is the province and 
the property of him who seeks to see and to understand the 
Unity of Nature. It is a thought which maybe pursued 
in every calling — in the busiest hours of an active life, and 
in the calmest moments of rest and of reflection. And if, 
in the wanderings of our own spirit and in the sins and 
sorrows of Human Life, there are terrible facts which resist 
all classification and all analysis, it will be a good result of 
our endeavors to comprehend the Unity of Nature, should 
it lead us better to see, and more definitely to understand, 
that which constitutes The Great Exception. 
I commend these chapters to the consideration, and I 
submit them to the criticism, of those who care for such 
inquiries. Like the former Work, of which this is a se- 
quel, some parts of it have appeared separately in another 
form. These have been reconsidered, and to some extent 
re-written ; whilst a new meaning has been given to the 
reasoning they contain by the place assigned to them in a 
connected treatise. 
The publication of it as a series of Articles, before its 
final appearance as a volume, will afford me, I hope, 
the advantage of hearing and of seeing what may be 
said and written of its errors or of its deficiencies. Per- 
haps, also, it may afford me an opportunity, before the 
whole of these Articles have appeared, of writing at least 
one more chapter on an important subject, for which leis- 
ure fails me now. 
I. 
GENERAL DEFINITIONS AND ILLUSTRATIONS OF THE UNITY OF 
NATURE — WHAT IT IS, AND WHAT IT IS NOT. 
The system of Nature in which we live impresses itself 
on the mind as one system. It is under this impression 
that we speak of it as the Universe. It was under the same 
impression, but with a conception specially vivid of its 
order and its beauty, that the Greeks called it the Kosmos. 
By such words as these, we mean that Nature is one whole 
— a whole of which all the parts are inseparably united — 
joined together by the most curious and intimate relations, 
which it is the highest work of observation to trace, and of 
reason to understand. 
I do not suppose that there is any need of proving this — 
of proving, I mean, that this is the general impression which 
Nature makes upon us. It may be well, however, to trace 
this impression to its source — to see how far it is founded 
on definite facts, and how far it is strengthened by such 
new discoveries as science has lately added to the knowl- 
edge of mankind. 
One thing is certain : that whatever science may have 
done, or may be doing, to confirni man’s idea of the unity 
of Nature, science, in the modern acceptation of the term, 
did not give rise to it. The idea had arisen long before sci- 
ence in this sense was born. That is to say, the idea existed 
before the acquisition of physical knowledge had been 
raised to the dignity of a pursuit, and before the method 
and the results of that pursuit had been reduced to sys- 
tem. Theology, no doubt, had more to do with it. The 
idea of the unity of Nature must be at least as old as the 
idea of one God ; and even those who believe in the deriva- 
tion of Man from the savage and the brute, cannot tell us 
how soon the Manotheistic doctrine arose. The Jewish 
literature and traditions, which are at least among the old- 
est in the world, exhibit this doctrine of the purest form, 
and represent it as the doctrine of primeval times. 
The earliest indications of religious thought among the 
Aryan races point in the same direction. The records of 
that mysterious civilization which had been established on 
the Nile at a date long anterior to the call of Abraham, are 
more and more clearly yielding results in harmony with the 
tradition of the Jews. The Polytheism of Egypt is being 
traced and tracked through the ready paths which led to 
the fashioning of many Gods out of the attributes of One. 1 
Probably those who do not accept this conclusion as his- 
torically proved may hold rather that the idea of the unity 
of Nature preceded the idea of the unity of God, and that 
Monotheism is but the form in which that earlier idea be- 
came embodied. It matters not, so far as my present pur- 
pose is concerned, which of these two has been the real or- 
der of events. If the law prevailing in the infancy of our 
race has been at all like the law prevailing in the infancy of 
the individual, then Man’s first beliefs were derived from 
authority, and not from either reasoning or observation. I 
do not myself believe that in the morning of the world The- 
! Rcnouf, “ Hibbert Lectures,” 1879. p. 89. 
