438 



NATL RE 



{March n, 1880 



that a new series of experiments should be carried out 

 on a smaller scale, with the object of finding out what 

 other circumstances, in addition to double loading, are 

 likely to cause these weapons to burst, and be a 

 greater danger to friends than to foes. The destruction 

 of the 100-ton gun is not calculated to increase con- 

 fidence in this combination of steel and iron, especially 

 when it is known that Armstrong and Woolwich guns 

 are built up on almost exactly similar experiments. In 

 addition to testing our own system in an exhaustive 

 manner, guns by other makers should be subjected to 

 exactly the same experiments, and if they yield better 

 results, should be adopted into the service. We have lately 

 seen that Sir William Palliser has subjected an old cast- 

 iron gun, lined with wrought-iron tubes, on his well-known 

 principle, to the test of double-loading with the most per- 

 fect success. Why should not the applicability of his 

 system to guns of the largest calibre be tested? If, as it 

 would appear, artillery officers are incapable of carrying 

 out these experiments in a scientific manner, they should 

 be assisted by outside talent, for the present state of 

 uncertainty ought not to be tolerated for a day longer. 



VEGETATION UNDER ELECTRIC LIGHT 



THE experiments which Dr. C. W. Siemens has made 

 in growing plants with the illumination of the elec- 

 tric light, and which were laid before the Royal Society 

 at its last meeting, were deservedly received with great 

 interest. In a country where the State does so little in 

 aid of the systematic prosecution of scientific inquiry, it 

 is impossible not to feel something more than apprecia- 

 tive when men like Dr. Siemens bring to its aid the 

 combined resources of wealth and technical knowledge. 

 England is rich in splendid gardens equipped with every 

 horticultural resource. But it is due to the fortunate 

 circumstance that the possessor of such a garden has 

 also paid great attention to the economic applications of 

 electricity, that experiments have been made, on a scale 

 never before attempted, which go a long way towards 

 proving that, as far as vegetation is concerned, all the 

 effects due to solar energy can be artificially produced. 



Anything connected with electricity has a peculiar 

 fascination for the public mind, and even in the discus- 

 sion which took place at the Royal Society, there was not 

 wanting the suggestion that there might be something — a 

 little inscrutable, perhaps — due to the electrical origin of 

 the source of light to which Dr. Siemens had subjected 

 his plants, which exercised an important influence on the 

 results. Such a feeling is of course likely to be still more 

 prominent in the minds of those who have paid no special 

 attention to the processes of plant-life, and who would 

 feel that almost all the interest of the matter was gone if 

 they were asked to eliminate the influence of electricity 

 from it altogether. Yet, obviously, this must be the case 

 directly Dr. Siemens' s results are studied in relation with 

 what has already been done in the same direction. 



The great physical fact on which all vegetable, and 

 therefore all other life, depends, is the breaking-up of 

 atmospheric carbon-dioxide by the green colouring matter 

 of foliage — chlorophyll, or leaf-green — under the influence 

 of light. How the thing is done is not known ; what is 



known is that it is accomplished by light, and that 

 chlorophyll is the means or instrument by which light is 

 able to effect the dissociation of carbon-dioxide which is 

 the indispensable precursor to the building up by the 

 plant of the various components of its tissues. The plant 

 is in consequence an accumulator of energy, and when 

 its substance is burnt this energy is liberated, and carbon- 

 dioxide — amongst other things — is again produced. 



Now the question which vegetable physiologists have 

 been asking themselves since the beginning of this 

 century is this : — Are these effects producible by light from 

 any source if of adequate intensity, or, as Sachs inquired 

 in 1865, are they to be attributed to some quality specially 

 inherent in solar light, and which cannot be artificially 

 imitated ? It is on this question that the real bearing of 

 Dr. Siemens's experiments is of importance. 



Closely connected with the conditions under which the 

 role of chlorophyll is performed, are those necessary to 

 its own production. Obviously as the plant grows, its 

 chlorophyll cannot remain a constant quantity ; and with 

 some trifling exceptions which do not affect the matter, it 

 may be laid down as an established fact that the same 

 conditions which are essential for the activity of chloro- 

 phyll, are also favourable for its manufacture. But it is 

 now known that chlorophyll may be developed under an 

 amount of illumination which is insufficient to bring its 

 functions into play. And this has been the difficulty 

 which the problem has all along presented. In 1806 

 A. P. De Candolle experimented with the light of six 

 Argand lamps ; he found that this was sufficient to 

 develop a green colour in etiolated leaves and also in 

 young seedlings of mustard and cress, but he completely 

 failed to obtain from perfectly healthy foliage any evolu- 

 tion of oxygen, and, therefore, any evidence that carbon- 

 dioxide had been broken up. In 1S60 Biot experimented 

 with a powerful illuminating apparatus (with two Argand 

 burners) which had been constructed for use in measuring 

 an arc of meridian in Spain. This also failed, and it was 

 suggested that the negative result of experiments with 

 lamp-light was attributable to its poorness in rays of high 

 refrangibility. The fact that these are most operative 

 chemically has led many persons to think, on purely <i 

 priori grounds, that they must play the most effective 

 part in the work done by chlorophyll. But repeated and 

 most careful experiment has shown that this is certainly 

 not the case. A long series of investigations, com- 

 mencing with those of Daubeny (1836), and taken up suc- 

 cessively by Draper (1844), Sachs (1864), and Pfeffer 

 ( 1 S7 1 ), have shown without a doubt that the yellow rays 

 are as effective in vegetable nutrition as those of all the 

 rest of the spectrum put together. 



The first experiment with the electric light in connec- 

 tion with vegetation was made by Hervc-Mangcn in 1S61. 

 He succeeded by means of it in developing chlorophyll 

 in young seedlings of rye, but he did not succeed in 

 demonstrating any chlorophyllian activity by the evolution 

 of oxygen. He found, however, thit the electric light 

 possessed one of the characteristic properties of sunlight 

 in producing heliotropism in plants exposed to it. While 

 it is found that the less refrangible rays of the solar 

 spectrum undoubtedly play the most important part in 

 the chemical work which is essential to plant life, the 

 more refrangible rays exercise what may be described as 



