130> 



• .KNOWLEPGE ,♦ 



[Dec. 1G, 1881. 



loik niaK!*.'s };«nerate,s niiormous quantities of oloctricity, 

 wliich iippcnra lus liiushw of liglitiiing issuing from the 

 roluiuii of steuiii above the crattir. The generation of tlie 

 steam within the molten ma.ss, and its con)pet<!nco to pro- 

 duce all volc4»nic phcnomeiKi, are ably diseus.sed hy Prof. 

 Judd from a thoroiigldy Kcicntitic .standpoint, and the 

 result of the diseussion ho gives us in the eardinal genc- 

 ndisutiou — the keynotf^ of modern vulcanology :-r"T]ie 

 v.inctl appe.irances prcscuted, alike in the grande.st and 

 tVeble.st outbursts, can all be referred to one simple cause, 

 viz., the escape from tlie midst of molten materials of 

 imprisoned atoani or water-gas." ^^ 



Now the presence of large quantities of water within 

 the recesses of the earth is by no means difficult to account 

 for ; but tlie cause of the inti'mtu heat is a far more diffi- 

 •ult and yet unsolved probU^m. .Y-'^^''*^"*^'"}' ''^^ taught us 

 tiuit the world is not, as was loi)g believed, a liquid mass, 

 surrounded by a thin solid shell. Sir Humphry Davy en- 

 deavoured to account for the heat of volcanoes on the 

 supposition that large quantities of uucomhined alkali 

 mcrtals oxist in the earth, which, when water finds its way 

 beneath the earth, violently decompose it, generating heat 

 and evolving hydrogen. Mr. Mallet considers that the 

 contraction of the earth's crust can develope enormous 

 <]nantitics of heat. It has been calculated that if a portion 

 nf the earth's crust, fifty miles in thickne.ss, were to have 

 its temperature raised 200° Fahr., the surface would be 

 raised by expansion more than a thousand feet. Moreover, 

 crumpled and distorted strata clearly prove that enormous 

 pressures have been exerted by contracting rock-masses. 

 Hopkins imagines that the earth has solidified both at the 

 centre and circumference, while cavities of molten matter 

 are distributed between them. Captain Dutton Iielieves 

 th.at lava is pressed to the surface by tlie weight of super- 

 incumbent rocks, and he admits that we cannot allow one 

 general reservoir, because lavas of dilTcrent composition 

 come from the same crater at different periods, and a lower 

 volcanic vent sometimes remains open, wliile the lava rises 

 and flows from a higher one. Soine have assumed that the 

 interior of the earth, although intensely heated, remains 

 solid on account of the enormous pressure, and that the 

 efl'ect of any local diminution of pressure is to lower the 

 fusing point, and thus cause the solid to become liquid. 

 Volcanic phenomena would thus ibe exliibited at the points 

 of diminished pressure. . , , 



But, although we seem to be as far as ever from deter- 

 mining the ultimate cause of volcanic efTects, the phenomena 

 themselves, as pre.scnted to our observation, .are far better 

 understood than heretofore ; and this is mainly due to two 

 causes, viz., the establisliment of seismological observatories, 

 and the microscopic study of erqptjye rocks. Of course, w-e 

 nmst add to these the applicati.o)j of moi-V; exact and scien- 

 tific m(!thods, and the advances due to the perfection of 

 .such uistrunicnts as the spectrosvppe and recording seismo- 

 meter, 'i'ho Vesuvius observatory was the first to be 

 (.itablishcd on anythiiig like a scientific basis, and several 

 valuable volumes of reports have l)een published by 

 its director, PalmierL For slxU'cn years, Tacchini, of 

 Palermo, and Silvestri, of Catania, have ui'ged the erec- 

 tion of an observatory near the' summit of Ktna, and, 

 tliaid<s to the liberality of the Italian Minister of Agricul- 

 ture and Commerce, and of the i^funicipality of Catania, it 

 is now aji acoouiplishcd fact, in .\\igust, 188l', the obser- 

 vatory will bo ready for use. It adjoins tlie site of the old 

 Ca.sa Ingl(!se, nearly 10,000 feet above the sea, and it is in 

 telegraphic communication with an observatory in Catania, 

 21 ft above the sea level, and also with observatories in 

 tlie seven principal towns upon the flaiJjs of the mountain 

 — Aci Reale, Randazzo, Paterno, Ademo, Bronte, Giarre, 



aind Linguaglossa. It will be furnished with all the most 

 approved metf;orological and seismologic^d instruments, 

 with spectroscopes, and with a fine refractor by Merz, of 

 Munich, the object glass of which, during the winter 

 months, will be tranKport«I to the Catania observatory and 

 mounted iji a similar toleiicopa Owing to the persevering 

 ellorts of Prof. M. S. di Ro.ssi, of Rome, who is the editor 

 of the IhtllHinc dfl Vulcaniamo JCaliaiio, seismological 

 oli.scrvations are now made in more than fifty towns of 

 Itfily, and although we could wish that they were better 

 f)rganised and placed under the control of some central 

 (jovcrnmcnt observatory in Rome, it cajinot be denied 

 that the Bulkdno (now in its .seventh year of publica- 

 tion) has placed on record a multitude of observations 

 of high intere.st to vulcanologists. Observatfiries are . 

 now lieing instituted in very distant volcanic centrea In 

 January la.st, Lord Granville forwardi-d to the Royal So- 

 ciety some valuable " notes on the earthquake of July, 

 1880, at Manila," by Commander W. B. Pauli, which 

 record the first scientific account of an eai"thquake in the 

 Philippine Islands. It occurre<l along the line of the Taal 

 volcanoes, and affected an area 220 mili-s by 7.5. The most 

 severe shock last(;d for 70 seconds, and combined oscilla- 

 tory, trepidatory, and rotatory movement. Some very in- 

 teresting engravings of pendulum curves accompany the 

 paper, which appears in the Proceedinf/s of the Royal Societi/ . 

 for February, 1881. The curves are of great complexity, 

 and show both the direction antl relative intensity of the 

 earthquake shocks, which were sometimes so violent that 

 the pendulum was jerked upwards from the paper, and thus 

 broke the continuity of the curve. Seismological instru- 

 ments, although far from perfect, have l>e<'n much improved 

 since the time when the patient student of vulcanology 

 contented himself with watching a lx>wl of treacle. The 

 electrical seismograph records tlie direction of the shock, 

 its intensity, and the moment of its occurrence and its . 

 cessation. Professor M. S. di Rossi has ingeniously applied 

 the microphone to the detection of the slight subterranean 

 noises which may be heard at any hour of the day or night 

 in some districts. He affirms that both in his observatory 

 in Rome, near the Ara C<i'li, and at Rocca di Papa, he has 

 often, while watching the point of a seismic pendulum in 

 a microscope and simultaueouly applying the telephone to 

 his ear, heard harsh sounds in the latter at the instant when 

 the pendulum has been seen to quiver. 



di{Ea:ms. 



, Bx ' Ep^i^^D OLObDl 



KEEPING in mind what has Tseen said about savage 

 mental philosophy, it is not surprising that the 

 inference drawn from the phenomena of ilreams is belief 

 in a double existence. Besides that waking self of wJbioh 

 the savage is hazily conscious, th(>re must be another nei/] 

 which, roaming the world while tlie body is at rest, sees and 

 does the things dreamed. Waliing, the savage knows, or 

 will be told, that wliat<'ver his dreams reveal to the con- 

 traiy, he has not moved from the place wliure he lay down ; 

 therefore it is that ghostrsoul — that ofh/;r self — which has 

 been away on the strange or familiar errand. And such, 

 belief in another self — 171 the body, yet at times not<)/"it — 

 is confirmed by daily experience. There are the suspensi«us, 

 of consciousness witnessed in swoon, apoplexy, catalepsy, 

 and other forms of insensibility. Then there are the. 

 phenomena of shadows and reflection, actual existences 

 to the savage, mocking doubles of liimself. The shadow 



