SCIENTIFIC SUMMARY. 
557 
The decomposition of chlorate of potash in the presence of oxides of 
manganese and copper has been studied by M. Wieaerliold. He found that, 
contrary to M. Schonbein’s hypothesis, oxygenated bodies are not the only 
ones capable of determining the decomposition, for that spongy platinum 
had the same power. A rise of temperature was found to take place in 
the mixture as soon as the bath in which the retort was placed had reached 
a temperature of 250° for the mixture of chlorate and peroxide of manga- 
nese, and 290° for the mixture with oxide of copper. Oxygen began to 
be given off at temperatures varying from 200° to 285°, according to the 
mixture employed. 
M. St. Clair Heville has made some interesting discoveries connected 
with the decomposition of bodies by heat. On passing a current of hydro- 
gen through a porous earthen tube, it diffuses so rapidly that the gas 
which issues from the other end of the tube will be found to be not 
hydrogen but air. If the porous tube is surrounded by a larger and 
shorter tube of glazed porcelain into which carbonic acid is passed at one 
end, the two gases will be found to have changed places by the time they 
reach the other end of the two tubes. 
When these tubes are heated to a temperature of 1,100° to 1,300° C., 
and a current of steam passed through the inner one, while a carbonic 
acid is passed through the outer tube, the gas collected consists of hydrogen 
and oxygen, mixed with carbonic acid. 
M. Deviile considers the decomposition of a substance to be in all 
respects analogous to the ebullition of a liquid ; water is completely 
decomposed at a temperature sufficient to expand the vapour to tenfold its 
volume at 0° C. The decomposition can also take place at lower tempera- 
tures, the phenomenon being in this respect analogous to that of the 
evaporation of liquids below their boiling points. M. Deviile has also 
extended his observations to the dissociation of carbonic acid by means 
of heat. 
GEOLOGY AND PALAEONTOLOGY. 
ROFESSOR RAMSAY has discussed the significance of the physical 
breaks and changes of life in the several strata of the Palaeozoic 
system. When he finds that strata have been upheaved, denuded, and 
had other rocks deposited upon them, he concludes that we here have 
evidence of an extremely long interval of time unrepresented by any 
deposit, the vast duration of which may be computed by noticing that the 
physical break is always accompanied by a change in the life ; hence, also, 
he supposes that a change in the life probably indicates a physical break. 
From the Lauvention rocks to the top of the Silurians are six of these 
cases of nonconformity ; in the Old Red Sandstone, two ; in the Carboni- 
ferous strata, one ; and one between the Carboniferous and Peruvian ; ten 
in all. Now, in no one of these strata is the duration so long that from 
bottom to the top all the species change ; yet in the breaks one commonly 
finds that not only have the species but most of the genera disappeared, 
