Intelligence and Miscellaneous Articles. 77 



definite chemical state. This substance presents variations and ano- 

 malies in its action which greatly influence the result. Those pho- 

 tographers, therefore, who may repeat the experiment will do well to 

 fix their principal attention upon this point. It is also requisite in 

 winter to warm the plates a little before placing them in the camera. 

 In pursuing this investigation, I have been much struck with the 

 wide field of research in experimental optics which it throws open. 

 By treating plates of albumened glass with different chemical solu- 

 tions, the most beautiful Newtonian colours, or " colours of thin 

 plates," may be produced. And it often happens that the landscapes 

 and pictures obtained by the camera present lively though irregular 

 colours. These not being in conformity with nature are at present 

 useless ; with this exception, nevertheless, that in many pictures I 

 have found the colour of the sky to come out of a very natural azure 

 blue. I hope soon to have the leisure requisite for pursuing this 

 very interesting branch of inquiry, and in the mean time I venture 

 to recommend it to the notice of your scientific readers. — Athenceum, 

 Dec. 6, 1851. 



ON COPPER CRYSTALLIZED BY MEANS OF PHOSPHORUS. 

 BY F. WOHLER. 

 The experiments of Bock and Vogel, sen., have taught us that 

 the whole of the copper in a solution of the sulphate contained in 

 closed vessels is reduced by phosphorus ; crystalline lamina? of greater 

 or less thickness, according to the duration of the reaction, having 

 the form of the piece of phosphorus and of a beautiful bright copper 

 colour, being formed. If the pieces of phosphorus are "placed in 

 contact with bright copper wires, reduction of the copper also takes 

 place upon them, and this in distinct, mostly well-formed octohedral 

 crystals, the form of which, when the process is allowed to continue 

 for weeks and months, with a quantity of undissolved crystals of the 

 sulphate in the solution, is distinguishable to the naked eye ; at the 

 same time the whole of the phosphorus disappears, and the' masses 

 of copper reduced by it are found filled inside with black pulverulent 

 phosphuret of copper. — Ann. der Chem. und Pharm. vol. lxxix. p. 126. 



ON THE ACCIDENTAL COLOURS WHICH RESULT FROM LOOKING 

 AT WHITE OBJECTS. BY M. D. M. SEGUIN. 

 1. If after having looked for some time at a white object the eyes 

 are closed, a coloured image of the object is seen. This image pre- 

 sents a number of colours, which change little by little : as an ex- 

 ample, I will narrate the following instance. After looking at a 

 very brilliant object, such as a white screen seen by the transmitted 

 light of the sun, on closing the eyes the image appears at the 

 first moment green, olive-green or yellow; but there is a red 

 border all round, followed by much darker tints. After a few mo- 

 ments the image becomes decidedly yellow, but the coloured border 

 approaches towards the centre of the image : the latter acquires a 

 deeper yellow, a zone of orange and a zone of red gain gradually 

 upon the yellow, and at the same time the dark tint which was 



