206 M. Niepce de Saint- Victor on some 



period of the year in which his artist operated on the Alps; 

 although it might be that from the high elevation of those 

 regions the operator was precisely in those atmospheric con- 

 ditions which exist on less elevated grounds during only cer- 

 tain months, on account of the density of the atmosphere that 

 the sun's rays have to penetrate. 



I shall not conclude this paper without expressing a wish 

 that M. Ed. Becquerel, M. Gaudin, Messrs. Foucault and 

 Fizeau, as well as Dr. Draper, will continue their researches, 

 and that we shall abstain from all discussion on this subject 

 until we have been able to verify the facts under all possible 

 circumstances. Time and only a few experiments will suffice 

 to settle the question. We are all animated with the wish of 

 arriving at the truth, and facts alone must now decide between 

 us. Whatever may be the result, we all can individually 

 congratulate ourselves on having contributed by our separate 

 labours to the explanation of the phsenomena of photography, 

 and to the advancement of this new and interestino; science. 



XXXI. Observations on some remarkable Properties of Iodine, 

 Phosphorus, Nitric Acid, &^c. Bi/ M. Niepce de Saint- 

 Victor*. 



On Iodine and its action. 



RELIEVE that I first discovered a property of iodine 

 which we should least expect it to possess, viz. that of 

 being attracted by the lilack parts of an engraving, ma- 

 nuscript, &c., leaving the white parts untouched. Thus, an 

 engraving is submitted to the vapour of iodine for about five 

 minutes at a temperature of from 60°to 70 F.; fifteen grammes 

 of iodine are required for each square decimeter (a longer 

 exposure is requisite at a lower temperature) ; this engraving 

 is then laid upon paper " sized " with starch, care being taken 

 to moisten it previously with water acidulated to 1° with 

 sulphuric acid. This is the only substance which as yet has 

 been found to give the impressions any degree of permanency : 

 however, they ultimately disappear on exposure to the air and 

 light; but by i;)asting them beneath a plate of glass, they may 

 be preserved for a ver^' long time. I'he proofs just alter 

 having been pressed with a ball of linen exhibit remarkably 

 distinct impressions, which on drying, however, become cloudy. 

 But what is still more remarkable is, that several copies of the 



* Translated from the Annates dc ( himie et de Physique for January 1848, 

 having been conimunicated in two parts to the Academic des Sciences the 

 22nd of June 1840, and 11th of JamiaiT 1847. 



