358 Prof. L. Moser on the so-called Calorotypes. 



It is that experiment in which I caused a seal to depict itself 

 on mercury with which a pure or silvered copper-plate had 

 been coated, and afterwards produced the image in the iodine 

 vapours. 



I now turn to the calorotypes of M. Knorr. As soon as I 

 had found from my experiments the fact that the actions of the 

 bodies were manifested without any elevation of temperature, 

 I operated at the ordinary temperature and never employed 

 heat, for the phenomenon appeared already to belong to a 

 somewhat complicated class, which needed not to be rendered 

 more intricate by the introduction of any foreign force. In 

 one case only did I depart from this rule, and that was in 

 order to determine the colour of the latent light of oxygen. 

 Since the affinity of several metals for this gas is increased 

 by heat, I warmed plates of copper and brass, on which the 

 invisible rays had acted, and on their becoming iridescent, I 

 obtained the images by means of the various colouring. I 

 communicated these results to several persons about the 1 8th 

 Sept. 1842, and among others to the Editor of these Annalen 

 (Prof. PoggendorfF), who had the kindness to bring them 

 before the notice of the Berlin Academy of Sciences, and to 

 cause their publication in the Monthly Proceedings*. Now 

 these are the calorotypes of M. Knorr, only, as I conceive, 

 obtained in a more advantageous manner; for M. Knorr 

 heats the plate with the body to be depicted on it until the 

 former becomes iridescent. The image which is formed under 

 these circumstances I have long been acquainted with, but 

 even now in my opinion it affords no proof. If, for instance, 

 a body is placed on the plate, at some points it will be in 

 contact, at others not ; the oxygen to which the iridescence 

 must be ascribed will be present in some places in sufficient 

 quantity, or have free access, at other points not ; moreover, 

 some parts of the plate will acquire a higher temperature on 

 being heated than the others, so that if after all we see the 

 image of a body on a plate, it may be owing to several cir- 

 cumstances. In my experiments I have avoided these, for I 

 allow the body in contact or at a distance to act first on the 

 metallic plates by its peculiar light, and then heat the plate 

 uniformly, the body to be depicted being absent, and the 

 oxygen having free access. I may therefore assert that the 

 calorotypes of M. Knorr are no new discovery, and that they 

 do not in the least alter the state of the case; for the conclu- 

 sions which might be drawn from the images produced by 

 iridescence I have already communicated, while M. Knorr 

 contents himself with the fact. 



* See Poggendorff's Annalen, vol. Iviii. 



