142 
Mr, Martyii J. Roberts on an 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, 
¥T 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, I 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. 
