ON THE INFLUENCE OF SOLAR RADIATION ON PLANTS. 373 
On the Influence of the Solar Radiations on the Vital Powers of Plants 
growingunder different Atmospheric Conditions .— Part II. 
By J. H. Gladstone, Ph.D ., F.R.S. 
Since I laid before the British Association my former Report, some of the 
experiments there detailed have been repeated, and the investigation has 
been pursued further in the same direction. I have the honour now to 
present the results which have been obtained. 
The experiments about to be described were conducted, not as before at 
Stockwell. but in Tavistock Square, London. The locality was not quite so 
favourable to the growth of plants, but they had always the advantage (un¬ 
less otherwise stated) of Btamliug on tables at the windows of a large upper 
room having a south-east aspect, so that they obtained the full benefit of 
tlio morning and noonday sun. The apartment was never artificially heated, 
hut in the winter time it must have beeu a few degrees higher in temperature 
than the external atmosphere. 
The coloured bell-glasses described in the previous Report were made use 
I am now able to give a more accurate description of what solar rays 
" ere actually transmitted by them. The effects of the different glasses on 
the prismatic spectrum were as follows:— 
Colourless glass. So perceptible difference from the normal spectrum. 
tellow glass. The red rays were cut. off, but the line C was just visible 
mtlie orange-coloured region. The yellow and green portions of* the spec- 
rum were quite natural, except perhaps that they were rather more uniform 
in colour than usual; the blue was rather brigbtabove the double line F, but 
icre was very little illumination in the portion more refracted, and the violet 
r ajs were quite unseen. The lines D, E, b, and F were very visible. 
tmglass. The spectrum consisted of two luminous spaces, separated by 
ro*ul band of perfect darkness. The one was of a red and orange colour, 
commencing between B and and apparently cut off by the dark line D. 
ic other was faintly illuminated with an olive-green tint, commencing about 
ie most intensely yellow part-of the ordinary spectrum, and continuing to 
ont (which was barely visible), and then passing into a lilac hue, which 
HnesF ° ft> ’ ^ became imperceptible perhaps a little below the 
The spectrum had a very singular appearance, consisting of 
MdmKi | ll 'ii Ct * ura ‘ nou8 bands. First there wur a reddish band of con- 
‘ - me brilliancy, occupying a space beyond that of the least refrangible 
vi rv r. ° •V Vls, bl e spectrum. This was separated by a dark space from a 
) narrow but bright band somewhere near the line B. Its colour was 
' \ e r ‘ ro,n an y of those of the normal spectrum, but perhaps it 
britrhf «ou nc , are9 I t tl p tbe oran K e ' Then, after another dark space, came a 
r„t Vw- n “ . K rea ter width, just above the line D, which, however, 
cut oH' ' ,'P erce Pbble* l he whole yellow portion of the spectrum was 
where ’/i . / ere " as n(l ‘humiliation (ill about midway between E and b, 
'dure »i,„ 1 6 rfcen suddenly appeared. This passed into a pale green, 
about Fnn' , W3S iltle ‘humiliation, but not perfect darkness, till at 
to the JJ ‘ ??f se bIue appeared, continuing through the region of the violet, 
F,mdrJr the m °1- r . e,ran S> b,e P° rtil '“ of the spectrum. The lines b, 
Th^,r vp ‘7 hist.net, as well as some about d and H. 
ilescriminn l*'* • , tran9n ‘‘ w «l by the various glasses, confirms the 
cuts off liv P f V1 ?, Usly S lven B>eir character, namely, that “Theblue glass 
y ar the greater portion of the luminous rays, but admits the 
