112 ART. 'à. — B. KOTO : 



ductivity, the melting point or the formation of complete melt being 

 1130°C. At 1300'^ a brisk effervescence or ' storm ' of gases occurred, 

 but not below. 



With the aid of the optical pyrometer of Holborn-Kuiibaum they 

 found in the field the temperature of the same lava, which in a red-hot 

 state filled up fissures, to be from 995° to lOéS'^C. The craAvling lava 

 stream was examined with the same at night, and it was found that the 

 bright (yellowish-red) j)i"Oximal portion was 995°, the dull (red) terminal 

 poiiion 857°, a temperature at which the rock becomes a little plastic. 



The writer believes that the lava-streams of Sakura-jiina be- 

 haved, and are still doing so, in the same fashion. Wolfl' (' Der 

 Vulkanismus,' Bd. I. p. 43) says, that foreign andésites begin to 

 be plastic at 1095" and melt completely at 1100^-1125^ 



Prof. K. Taw AR A, of the Engineering College carried on, at the 

 writer's request, a melting experiment at fixed temperatm'es and for de- 

 finite lengths of time, the action being suddenly interrupted by quench- 

 ing the samples in water at 16°. The high temperatures were determined 

 with a thermoelement. The original rock-specimens Avere collected by 

 Prof. F. Omori from the second period flow of 1912 in the same crater 

 of Osliima island. The lava samples of hypersthene- andésite entrusted 

 to the writer for microscopic analysis are slaggy and black, and dotted 

 with bytownite-phenocrysts. They possess hyalocrystalline texture witli 

 microphenocrysts of hypersthene. The groundmass is built up of 

 feldspar microlites and augite grains, cemented by brown glas:^ Avhich 

 contains dentritic skeletal magnetite. 



The slides made of the quenched test samples were seen under the 

 microscope with the following characteristics : 



No. 1. liaised to 900° and kept at this te,inperature for 1 hour. 

 Not nuicli change from the original specimen. 



No. 2. 900", 2 hours. Dentritic magnetite is still io hv seen. 

 Augite in the groundmass is partially I'used, forming black glass. 



