138 REPORT—1850. 
been attributed to Light.’ In this paper a number of experiments are brought 
forward to prove that all the effects produced upon metallic solutions by bright 
sunshine can be obtained by a prolonged exposure to a temperature of 210° 
Fahrenheit. We are now, however, in a position to show that the chemical 
effects produced by rays of dark heat are of a very different character from 
those usually attributed to light. Mr. Robert Harrup. in a communication to 
Nicholson’s Journal in 1802, refuted the experiment of Count Rumford, show- 
ing that several salts of mercury were reduced by light alone, and not heat. 
In 1801 Ritter of Jena* demonstrated the existence of rays beyond the 
spectrum which have no luminous power, but which exhibited very active che- 
mical agencies. Ritter stated that the red rays had the power of restoring 
darkened muriate of silver to its original colour, and he infers therefore the 
existence of two sets of invisible rays, the least refrangible favouring oxygena- 
tion, while the most refrangible on the contrary deoxidize. Similar results to 
these have since been obtained by Sir John Herschel, and more recently still 
by M. Claudet. Bockman about the same time observed that the two ends 
of the spectrum acted differently on phosphorust+. 
Desmortiers in 1801 published a paper in Gilbert’s Annals, entitled ‘ Re- 
cherches sur la Décoloration spontanée du Bleu de Prusse’, subsequently 
translated into Nicholson’s Journal, in which he has mentioned the influences 
of the solar rays in producing the change. 
About the same time Dr. Wollaston { examined the chemical action of the 
rays of the spectrum, and arrived at nearly the same results as Ritter. He 
states, ‘‘ This and other effects usually attributed to light are not in fact 
owing to any of the rays usually perceived.” 
Attention having been directed by Dr. Priestley in 1779 to the influence of 
light on plants, numerous inquirers were started on this track, and the valuable 
researches of Senebier, Ingenhousz, DeCandolle, Saussure and Ritter§ were 
the result. These are already too well known to require anything beyond 
this incidental notice; but in 1801 Labillardiére communicated to the Phi- 
lomathic Society his discovery that light was necessary to the development 
of pores in plants, and subsequently we find Victor Michellotti of Turin, in a 
paper, ‘ Experiments and Observations on the Vitality and Life of Germs|l,’ 
stating ‘‘ that light has a decided action on those germs which are exposed to 
it, that this action is prejudicial to them, and it manifests its action by re- 
turding their expansion if the light be weak, or a reflected light; er by the 
total extinction of their life, if it be very intense, as that which comes directly 
from the sun.” 
M. Macaire Prinsep again states, ‘‘ that sheltering leaves from the action 
of light prevents their change of colour in the autumn ; that if the entire leaf 
was placed in the dark, it fell off green; if only a part, the rest of the paren- 
chyma changed colour, and the covered portion retained its original colour.” 
‘Those appear to be the more important researches in connexion with this 
particular section of the inquiry, until the correction of the statements of 
Saussure were published by Dr. Daubeny, who satisfactorily proved that 
* Nicholson’s Journal, August 1804, + Voigt’s Maazgine, vol. iv. 
1 Philosophical! Transactions, 1802, p. 379. . 
§ Senesrer. Expériences sur l’Action de la Lumicre Solaire dans la Végétation. Paris, 
1788. 
IncenHOUSZ. Expériences sur les Végétaux. Phil. Trans. 1782. 
Decanpotte. Mémoires des Savans Etrangers, vol. i. 
Saussure. Recherches Chimiques sur la Végétation. Annales de Chimie, vol. 1. 
Ritter. Gehlen, Journ. der Chem., vol. vi. 
|| Journal de Physique, Ventose, an 9. i 
4 Mémoires de la Société de Physique et d’Histoire Naturelle de Genéve, tom. iv. p. 1. 
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