Intelligence and Miscellaneous Articles. 151 



account of the submarine topography of the area east of North 

 America, and summarizes Dr. J. W. Spencer's work upon a 

 submerged Antillean continent ; he then deals with the effects 

 which would be produced upon the Gulf Stream by the uprising of 

 this continent in the Glacial Period, and maintains that, as the 

 current could not pass into the Gulf of Mexico (being debarred 

 by a coast of high continental land), it would flow directly north- 

 wards into the North Atlantic, and thereby be deprived of about 

 10° (Fahr.) of heat : the effects of which may be practically 

 illustrated by supposing the isothermal line of 32° to take the 

 place of that of 42° in the northern hemisphere. He argues that 

 the increased snowfall which would thus be caused over certain 

 areas would tend to intensify the cold through all the adjoining 

 tracts. 



To the effects produced in this way must be added those due to 

 the elevation of the land of Eastern North America and to an 

 elevation of North-western Europe, which is supposed to have 

 occurred at the end of Pliocene times. These elevations would 

 intensify the glaciation caused by the difference of direction taken 

 by the Gulf Stream. 



2. ' On the Affinities of the Echinothuridae, and on Pedinothuria 

 and Elikodiadema, two new subgenera of Echinoidea.' By J. W. 

 Gregory, D.Sc., E.G.S. 



3. ' On Echinocystis and Palceodiscus, two Silurian Genera of 

 Echinoidea.' By J. W. Gregory, D.Sc, E.G.S. 



XXV. Intelligence and Miscellaneous Articles. 



ON THE EXPLOSION OF THIN LAYEKS OF EXPLOSIVE GASES. 

 BY PROF. F. EMICH. 



r PHE observation that the small electrical sparks produced by 

 -■- shaking mercury in glass vessels frequently do not ignite 

 detonating gas, led the author to investigate the lengths of the 

 shortest sparks which can ignite explosive gas mixtures under 

 various conditions. 



The electrodes between which the spark passed were so con- 

 structed that their distance apart at the moment of explosion was 

 identical with the distance in which the explosion could just travel. 



For pure detonating gas this thickness under normal conditions 

 was found to be - 22 millim. For other conditions experiments 

 gave the following results : — 



1. It is approximately inversely proportional to the pressure of 

 the gas — that is, to the concentration. 



2. It increases somewhat with increase of temperature. 



3. If detonating gas is mixed with hydrogen, nitrogen, or car- 



