SEPTEMBER 14, 1899] 
aclear sky. The total amount of incident energy represented 
by the whole area of the curve is 1°7 calories per square 
centimetre per minute, or 1,020,000 calories per square metre 
per hour. 
I have drawn a thick black vertical band in the red end of 
the spectrum corresponding in position and breadth with the 
principal absorption band of chlorophyll as seen in a green leaf. 
By integration it may be shown that the area of this part of the 
curve is about 6°5 per cent. of that of the whole curve, so that 
this value represents something like the theoretical maximum 
efficiency of a leaf in bright vertical sunshine, supposing the 
conditions could be made so favourable as to result in a com- 
plete filtering-out and utilisation of the whole of the rays of the 
right period for producing decomposition otf carbon dioxide. 
This maximum efficiency expressed in calories per square 
metre per hour is 66,300, corresponding to the heat of formation 
of about 16°5 grams of carbohydrate. Under the most favour- 
able conditions we have employed up to the present we have 
not obtained a larger production than about 3°0 grams of carbo- 
hydrate per square metre per hour, or about 18 per cent. of the 
theoretical maximum ; but this was in air containing only 16°4 
parts of carbon dioxide per 10,000, which must be very far 
below the true optimum amount. 
The brilliant discoveries of recent years on the constitution 
and synthesis of the carbohydrates have not brought us sensibly 
nearer to an explanation of the first processes of the reduction 
of carbon dioxide in the living plant. The hypothesis of Baeyer 
still occupies the position it did when it was first put forward 
nearly thirty years ago, although it has, it is true, received a 
certain amount of support from the observations of Bokorny, 
who found that formaldehyde can, under certain conditions, 
contribute to the building up of carbohydrates in the chloro- 
lasts. 
3 The changes which go on in the living cell are so rapid, and 
are of such a complex kind, that there seems little or no hope 
of ascertaining the nature of the first steps in the process unless 
we can artificially induce them under much simpler conditions. 
The analogy which exists between the action of chlorophyll 
in the living plant and that of a chromatic sensétiser in a photo- 
graphic plate, was, I believe, first pointed out by Captain 
Abney, and was more fully elaborated by Timiriazeff, who was 
inclined to regard chlorophyll as the sensitiser par excellence, 
since it absorbs and utilises for the assimilatory process the radi- 
ations corresponding approximately to the point of maximum 
energy in the normal spectrum. The view which Timiriazeff 
has put forward, that there is a mere physical transference of 
vibrations of the right period from the absorbing chlorophyll to 
the reacting carbon dioxide and water, is, I think, far too 
simple an explanation of the facts. Chromatic sensitisers have 
been shown to act by reason of their antecedent decomposition 
and not by direct transference of energy, and the same probably 
holds good with regard to chlorophyll, which is also decomposed 
by the rays which it absorbs. We must probably seek for the 
first and simplest stages of the assimilatory process in the inter- 
action of the reduced constituents of the chlorophyll and the 
elements of carbon dioxide and water, the combinations so 
formed being again split up in another direction by access of 
energy from without. 
The failure of all attempts to produce such a reaction under 
artificial conditions is, I think, to be accounted for by the 
neglect of one very important factor. We are dealing with a 
reaction of a highly endothermic nature, which is probably also 
highly veverszb/e, and on this account we cannot expect any | : 
| secretaries, 
sensible accumulation of the products of change unless we 
employ some means for removing them from the sphere of 
action as fast as they are formed. 
In the plant this removal is provided for by the living 
elements of the cell, by the chloroplast, assisted no doubt by 
the whole of the cytoplasm. We have here, in fact, the 
analogue of the chemical sensitisers of a photographic plate, 
which act as halogen absorbers, and so permit a sensible 
accumulation of effect on the silver salts. 
When we have succeeded in finding some simple chemical 
means of fixing the initial products of the reduction of carbon 
dioxide, then, and then only, may we hopefully look forward to 
reproducing in the laboratory the first stages of the great 
synthetic process of nature on which the continuance of all life 
depends, 
NO. 1559, VOL. 60] 
NATURE 
483 
NOTES. 
THE Allahabad Proncer Maz? understands that Mr. J. N. 
Tata, of Bombay, has determined to dissociate his offered 
endowment for a scientific research institute in India from the 
proposed family settlement, which was one of the original con- 
ditions, as the latter part of the scheme presented insuperable 
difficulties. With great generosity and public spirit Mr. Tata 
has declared his intention of making his offer, which amounts, 
it will be remembered, to some thirty lakhs of property, quite 
unconditional. He is now preparing, in consultation with the 
provisional committee, a revised scheme for submission to 
Government. In preparing it, he and the provisional committee 
will utilise all the information and advice they have received 
from all parts of India in response to the circulars issued some 
months ago, and there is good prospect of a practical plan being 
evolved. 
THE forty-eighth annual meeting of the American Associ- 
ation for the Advancement of Science was held at Columbus, 
Ohio, on August 19-26, under the presidency of Dr. Edward 
Orton, of Ohio State University. There were 350 members 
and associates present, and 273 papers were communicated to: 
the sections. The address of the retiring president, Prof, F. W. 
Putnam, of Harvard University, was published in last week’s 
NaTuRE, and portions of the addresses delivered by presidents 
of the sections will appear at the earliest opportunity. The 
subjects of these addresses are :—Section of Mathematics and 
Astronomy, ‘‘The Fundamental Principles of Algebra,” by 
Prof. A. Macfarlane; Section of Mechanical Science and 
Engineering, ‘‘ Engineering Education as a Preliminary Train- 
ing for Scientific ,Research Work,” by Prof. Storm Bull ; 
Section of Zoology, ‘‘The Importance and the Promise in the 
Study of the Domestic Animals,” by Prof. Gage; Section of 
Geology and Geography, ‘‘The Devonian in Canada,” by 
Mr. J. F. Whiteaves; Section of Physics, ‘‘The Field of 
Experimental Research,” by Dr. Elihu Thomson; Section of 
Chemistry, ‘‘ Definition of the Element,” by Prof. F. P. Venable ; 
Section of Botany, ‘‘ The Progress and Problems of Plant Physi- 
ology,” by Prof. Barnes ; Section of Anthropology, ‘‘ Begin- 
nings of the Science of Prehistoric Anthropology,” by Prof. 
Wilson. Prof. C. E. Munroe delivered a popular lecture on 
“© Applications of Modern Electricity.” New York was selected 
as the place of meeting next year, and Prof. R. S. Woodward, 
Columbia University, was nominated president. 
A VERY successful congress of mining engineers was held at 
Teplitz, in Bohemia, on September 4-8. It was attended by 
400 mining engineers from all parts of Austria and by a few 
representatives of other countries, Great Britain being repre- 
sented by Mr. H. Bauerman, Mr. Bennett Brough and Mr, 
D. A. Louis. Mr. Gottfried Hiittemann, of Briix, was elected 
president; Mr. J. Gleich, of Klagenfurt, and Prof. Clemens 
| Winkler, of Freiberg, vice-presidents ; and Prof. J. von Ehren- 
werth, of the Przibram School of Mines, and Mr. M. Heinsius, 
Papers were read by Prof. Clemens Winkler, on 
the history of combustion with reference to the duration of the 
world’s coal supply ; by Prof. Otto Frankl, of Prague, on sug- 
gested reforms in mining law; by Mr. H. Locker, of Briix, on 
water-inbursts in the Diix-Ossegg collieries and their influence 
on the Teplitz hot-springs; and by Mr. A. Bloemendal, of 
Vienna, on the electric transmission of power in mines. It was 
decided that the next mining congress should be held in Vienna 
in four years’ time. In connection with the congress, excursions 
were arranged to the brown coal mines of the Briix Coal Co. 
and of the Bruch Coal Co., to the Teplitz rolling mills, to the 
Aussig chemical works, to Edmundsklamm and other points of 
geological interest in the Bohemian Switzerland, and to the 
