142 Mr, Martyn J. Roberts on cm anomalous 



It is necessary I should state that the results are likely to 

 be differently recorded by different observers, unless the 

 same photographic preparation is used in all cases. I have 

 been in the habit of using a paper washed with a solution of 

 the muriate of baryta and nitrate of silver, while it is yet damp. 

 The sensitiveness of this preparation may be shown by the 

 fact of its being acted on very decidedly in five minutes by a 

 gas flame from a ten-holed Argand burner. On this paper 

 the tints are blue under greenish glasses, while under those 

 inclining to a yellow they are reddish. If a paper prepared 

 with a solution of the chloruret of soda be used, the tints are 

 reddish under the green, and bluish under the pure white or 

 yellowish glasses. 



The above list does not contain all the bodies I have ex- 

 amined, but they are all I am satisfied to place in a determi- 

 nate position. 



Not having deduced any fixed principles from my observa- 

 tions, I may appear to act prematurely; but as it is probable 

 the same subject may be engaging those whose minds and 

 means are superior to my own, and as it is possible even my 

 humble experiments may be of service to such persons, I feel 

 myself excused from the charge of obtrusiveness. 



12, Cornwall Street, Devonport, January 2, 1840. 



XXVI. On an anomalous Electric Condition of Iron. By 

 Martyn J. Roberts, Esq. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 TT is now some months since, that while prosecuting a series 

 *- of novel galvanic experiments, I discovered a singular 

 anomaly in the electric condition of iron, which is, that 

 although iron if associated with copper as a galvanic pair is 

 highly positive to the copper, yet when associated with zinc, 

 it is more highly negative to the zinc than copper would be 

 under similar circumstances; or in other words, that although 

 copper and iron form a galvanic combination, in which the 

 iron is in the same relation to the copper that a zinc plate 

 would be, yet that iron and zinc form a galvanic pair that has 

 a greater power of generating electric action than a similar 

 sized pair of copper and zinc. This singular phaenomenon 

 will, 1 believe, lead the way to some important discoveries; 

 but not to occupy too much space in your valuable Journal, 

 I will without further comment give extracts from my note- 

 book of some experiments made by me on this subject. 



