June 26, 1879] 



NATURE 



199 



first of these mounds, and then divided into two branches' 

 one of which commenced to flow towards Aderno, and the 

 other towards Biancavilla, but the supply died out at the 

 source, and the new streams solidified at a height of 2,ocx3 

 metres, having flowed for a mile and a quarter as a 

 stream 400 metres in breadth. This stream did but little 

 damage ; it did not penetrate into the cultivated region, 

 and but in short distance into the woody region. It came 

 into contact, however, with a bed of snow, part of which it 

 converted into clouds of steam, while another portion was 

 liquefied and rushed down the sides of the mountain in a 

 foaming torrent, carrying with it a good deal of debris. 



The outflow of lava ceased on the south side of the 

 mountain, because the lava found a vent at a lower level 

 on the north side. As the one decreased in activity the 

 other increased. On May 28th Silvestri visited the scene 

 of the northern eruption. A great column of smoke 

 appeared about 20^ east of north, while a shower of sand 

 descended, producing the " sad leaden light " (la luce 

 triste plumbed) observable during an eclipse. More than 

 two pounds of this sand were collected in ten minutes in 

 an inverted umbrella, and the north flanks of the moun- 

 tain were soon covered with it. Silvestri ascended from 

 Randazzo towards the new craters, and when at a height 

 of about 2,000 metres and near Monte Nero he heard loud 

 subterranean detonations, and perceived severe oscillations 

 of the soil. Soon afterwards he came upon the great rift, 

 together with several smaller ones, converging towards 

 the principal crater. In the immediate neighbourhood of 

 Monte Nero and Timpa Rossa three new craters were 

 seen, from one of which dense clouds of white smoke 

 issued, while the others emitted lava and showers of ashes 

 and incandescent stones. Frequent flashes of lightning 

 issued from the smoke. The stream of lava near its 

 source emitted a very bright light which, when viewed by 

 a direct vision spectroscope, gave the lines of hydrogen, 

 calcium, sodium, and potassium. The lava flowed down- 

 wards at a rapid rate : the wood of CoUebasso was de- 

 stroyed, and by the evening of May 29 it had flowed 

 f>\ rniles, destroying the bridge of Passo Pisciaro and 

 crossing the postal road between Randazzo and Lingua- 

 glossa. On Sunday the 31st the stream was rapidly ap- 

 proaching Mojo ; the inhabitants became frightened, and 

 brought out the figure of their patron Saint Antony, 

 which was carried in procession to the edge of the stream, 

 while the people fell on their knees and besought the 

 Deity to save them from [the impending danger. After 

 the evening of June i the force of the eruption began 

 somewhat to abate,>nd by the 6th inst. it was practically 

 at an end. The lava stream ran nearly 7 miles from its 

 source, and ultimately stopped 500 yards from the river 

 Alcantara, and about half a mile from the village of Mojo. 

 At its termination it is 23 feet in breadth and nearly 32 

 feet in height. The lava stream entered the bed of the 

 Pisciaro torrent with a velocity of from 4 to 5 metres a 

 minute, which was reduced to 2 metres a minute in the 

 lower valley of less inclination. In 76 hours the lava 

 flowed more than six miles from its source. 



Indications of a disturbed volcanic condition were 

 manifest last October, when powerful shocks of earth- 

 quake were felt in the territory of Mineo, Palagonia, Viz- 

 zini, Scordia, Militello, and Caltagirone. Mineo was the 

 centre of disturbance, and here the shocks continued at 

 intervals dunng the month of October. Loud subterranean 

 noises were also heard at intervals. Two months later an 

 eruption of mud and gas took place near Paterno, on the 

 southern flanks of Etna. The mud was hot, salt, and 

 petroleum-bearing {fane;o salato termale petroleifero), and 

 Its ejectment continued for several months. Towards the 

 end of December last the whole eastern sea-board was 

 visited by a strong shock of earthquake ; and soon after- 

 wards a great increase of smoke from the central crater 

 of Etna showed that the dynamic activity of the moun- 

 tain was unusually near the surface. 



- Even now we cannot regard the eruption as at an end 

 Ten days after the cessation of the flow of lava telegrams 

 from Rome (dated June 17) announced that the neigh- 

 bourhood of Santa Venere and Guardia had been visited 

 by repeated shocks of earthquake. A telegram on the 

 following day announced that " an earthquake of great 

 riolence" had occurred near Aci Reale, destroying five vil- 

 lages. There is evidently a great deal of volcanic energy 

 still pent up not far from the surface, and we must fear 

 that before long a further outburst will relieve the im- 

 prisoned Titanic forces. G. F. Rodwell 



THE ELECTRIC DISCHARGE WITH THE 

 CHLORIDE OF SILVER BATTERY^ 

 II. 

 The History of a Tube 

 No. 129, Hydrogen 

 ■\17'E now give an account of the very great variety of 

 * ^ phenomena presented by the same tube charged 

 with hydrogen. No. 129 (see Plate), under different condi- 

 tions of exhaustion when used in connection with batteries 

 of various potentials, and traversed by currents of difTerent 

 strengths. 



This tube is 32 inches long and i "6 inch in diameter, 

 the terminals are a straight wire and a ring, about i 

 inch in diameter, both of aluminium ; it is furnished with 

 a glass stop-cock at each end, as represented in Fig. 3. 

 The glass stop-cocks are connected with the mercurial 

 pumps (Alvergniat and Sprengel) and with the gas gene- 

 rator respectively, as shown in Fig. 5. 



Tube 129, ^tk Charge of Hydrogen. — A glow at both 

 terminals was first seen when the pressure was i7"2 mm., 

 22,632 M,^ with 8,040 cells, and great heat developed in 

 the dark discharge near the middle of the tube. The 

 spectroscope showed faintly the C and F lines. 



Pressure i6'5 mm., 21,710 M, 8,040 cells. One 

 luminosity like that on the right hand of Fig. 10, sho 

 out from the positive and approached to within 6 inches 

 of the negative, then receded back and disappeared. 



P 



1:^11 crj cr=s 



Fig. 10. 



Pressure i5'8 mm., 20,789 M, 8,040 cells. 3 luminosi- 

 ties, very steady, which moved slowly and steadily towards 

 the negative. The tube hottest in dark part where there 

 was probably a non-luminous entity. 



Pressure 14 mm., 18,421 M, with 6,840 cells, the current 

 was unsteady, but it was perfectly steady with 8,040, and 

 6 arrow-headed luminosities like that on the left of Fig, 

 1 1, were produced and soon disappeared. 



Fig. II. 



Pressure io'3 mm., I3,S52' M, with 8,040 cells. 8 

 luminosities something like i. Fig. 12. 



Pressure 9'4 mm., 12,368 M> with 8,040 cells. 12 

 luminosities like those. Fig. 7 in the Plate. The C and F 

 lines seen in the glow around the negative. 



Pressure 77 mm., 10,132 M, with 8,040 cells. 10 

 luminosities like Fig. 6 in the Plate ; these ran together 

 and disappeared and reappeared in a few seconds. 



* Continued from p. 178. 

 » M = millionths of an atmosphere 



