100 
Professor Renault lias been so fortunate as to have ob- 
tained a fine collection of specimens in a most perfect state 
of preservation from Autun, and they could scarcely have 
fallen into better hands. After describing them at length 
he comes to the following conclusion : 
“ D’apres ce qui precede, il est done a pen pres certain que 
ces petioles de Myelopteris sont des petioles de Fougeres, 
ayant eu le mode de croissance et le port actuel de nos 
Angiopteris, dont ils differaient pourtant a certains dgards, 
et Ton pent les consid^rer comme ayant form^ un genre 
d’une grande importance a Tepoque carbonifere, mais actu- 
ellement compldtement dteint, que Ton doit ranger dans la 
famille de Marattiees.” 
Further Observations and Experiments on the Influence 
of Acids on Iron and Steel,” by William H. Johnson, B.Sc. 
At the last meeting of the Society Professor Reynolds 
in an interesting paper “ On the Effect of Acid on the Inte- 
rior of Iron Wire,” appears to think that I did not attribute 
to hydrogen any portion of the remarkable change produced 
in iron and steel by immersion in acid. That immersion in 
acid is the primary cause no one, I think, will dispute ; but 
that hydrogen plays an important part in producing these 
changes and is the cause of the bubbles, the following para- 
graph from a paper I read before the Society, March 4th, 
1873, will prove : 
“The experiments of Professor Graham in 1867, and 
more recently those of Mr. Parry, show that hydrogen, car- 
bonic oxide and carbonic acid, and nitrogen, are evolved 
from wrought iron, cast iron, and steel, when heated in 
vacuo. Therefore it seems probable that a part of the 
hydrogen produced by the action of the acid on the iron 
may be absorbed by the iron, its nascent state facilitating 
this. And when the iron is heated by the effort of breaking 
it, the gas may bubble up through the moisture on the 
fracture,” 
