TRANSACTIONS OF THE SECTIONS. 35 
prepared: good writing-paper is washed over with a solution of the sulphate of cop- 
per and partially dried ; it is then washed with a solution of the bichromate of pot- 
ash and dried at a little distance from the fire. Papers thus prepared may be kept 
for any length of time, and are always ready for use. They are not sufficiently sensitive 
for use in the camera obscura, but they are available for every other purpose. An en- 
graving—botanical specimens or the like—being placed upon the paper in a proper 
photographic copying-frame, it is exposed to sunshine for a time, varying with the in- 
tensity of light from five to fifteen or twenty minutes. The result is generally a 
negative picture, This picture isnow washed over with a solution of nitrate of silver, 
which immediately produces a very beautiful deep orange picture upon a light dun 
colour, or sometimes perfectly white ground. This picture is quickly fixed by being 
washed in pure water and dried. The author remarked that, if saturated solutions 
were used, a negative picture was first produced, but if the solutions were diluted with 
three or four times their bulk of water, the first action of the sun’s rays was to darken 
the paper, immediately upon which a very rapid bleaching action followed, giving an 
exceedingly faint positive picture, which was brought out in great delicacy by the 
nitrate of silver. It is necessary that pure water should be used for the fixing, as the 
presence of any muriate damages the picture, and hence arises another pleasing vari- 
ation of the chromatype. If the positive picture be placed in a very weak solution of 
common salt, the images slowly fade out, leaving a very faint negative outline. If it 
be taken from the solution of salt and dried, a positive picture of a lilac colour may be 
produced by a few minutes’ exposure to sunshine. Prismatic analysis has shown that 
the changes are produced by a class of rays, which lie between the least refrangible 
blue, and the extreme limits of the violet rays of the visible prismatic spectrum—the 
maximum darkening effect being produced by the mean blue ray, whilst the bleaching 
_ effect appears to be produced with the greatest energy by the least refrangible violet 
‘rays, 

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On the Influence of Light on the Growth of Plants. By R. Hunt, 
___ The peculiar influence exerted upon the germination of seeds, and the growth of 
_ the young plants by coloured light, has been for some years the subject of the author’s 
investigations. The results show the surprising powers exerted by the more luminous 
rays in preventing germination, and in destroying the healthful vigour of the young 
_ plant. Plants, when made to grow under the influence of the red rays, bend from 
the light as something to be avoided; while the blue or chemical rays are efficacious 
in quickening the growth of plants. Since the publication of the last Report, the 
author has tried plants of a great variety of kinds, and the same effects have been 
Ba iced. It has, however, been found, that although blue light accelerates ger- 
“mination, and gives a healthful yigour to the young plant, its stimulating influences are 
- too great to ensure a perfect growth, The strength of the plant appears to be ex- 
bended in the production of a beautiful deep green foliage ; and it is only by checking 
his tendency, by the substitution of a yellow for a blue light, that the plant can be 
rought into its flowering and seeding state, The etiolating influence of the green 
_ Yays was observed, as well as the power which plants possessed of sending out 
i shoots of a great length, in search of that light which is essential to their vigour, © 



On the Influence of Light on a great variety of Metallic and other Com- 
= pounds. By R. Hunt, 
a The author, having briefly detailed the numerous discoveries in this branch of in- 
quiry, from the time of the alchymists to the present day, proceeded to describe the 
results of his experiments, made with nearly every variety of ‘chemica] combination. 
‘Tt was not with the view of establishing any theory relative to the solar agency, that 
7 this matter was brought before the Section, but merely to put upon record a great 
: “number of facts, which appear to prove the constant acting of the sun’s rays upon all 
_ bodies, and to show the boundless extent of this inquiry. It has been shown by Petit, 
~ that light influences the arrangements of crystals. Labillardiére and Michelotti have 
shown the necessity of light to the development of pores in plants, and its injurious 
“influence on young plants and animals. The experiments of Ritter and others, down 
— | ai Slo | D2 






