May 1, 18!J1.] 



KNOWLEDGE 



89 



distances. Eecent researches show that fine volcanic duat 

 is universally distributed over the sea. The darkness so 

 frequently mentioned in accounts of eruptions is caused 

 entirely by clouds of volcanic dust obscuring the daylight. 

 The red clay deposits in the deepest and most remote 

 parts of the ocean are now considered to be chiefly com- 

 posed of oxidized volcanic dust. 



Portions of liquid, or semi-liquid, lava are caught up by 

 the steam and hurled into the air. These assume a more 

 or less spherical form, and are known as " bombs." At a 

 distance they give the appearance of flames. And here 

 we may remark that the flaring, coloured pictures of Etna 

 or Vesuvius in eruption, which frequently may be seen, 

 are by no means correct. The huge flames shooting 

 up into the air are imaginary — another case of a 

 popular fallacy — but probably suggested by the glare 

 and bright reflection from incandescent lava down in 

 the crater. 



But there is another way in which a good deal of fine 

 volcanic dust, or ash, is produced ; and it is this— the 

 lava is so full of steam intimately mixed up with it that 

 the steam, in its violent escape, often blows the lava into 

 mere dust. This might be illustrated by the cloud of 

 spray seen for a moment after a soap-bubble has burst ; 

 and we can well imagine that something like this takes 

 place in a boiling and seething mass of lava in a crater 

 during eruption. The steam, we ought to mention, is not 

 dissolved in the lava, but absorbed by it, and is said to 

 be "'occluded" (hidden away). 



When lava-flows take place the lava does not always 

 come from the crater, but often issues firom the side of 

 the volcano. This marks the crisis of the eruption, and 

 now a gentle decline sets in. The volcanic forces have 

 done their worst, and the lava-column begins to sink. 

 Explosions decrease in violence, less ash is ejected, and 

 finally cinders choke up the orifice ; and so the volcano, 

 as it were, chokes up itself. 



So great is the force of the pent-up steam trying to 

 escape that it frequently blows a large portion of the top 

 of the volcano bodily away, leaving only a truncated cone ; 

 and, in some cases, a whole mountain has been thus 

 blown to pieces. Finally, torrents of rain follow or 

 accompany the upthrust of so much steam into the air. 

 Vast quantities of volcanic ash are caught up by the rain, 

 and in this way large quantities of mud are washed down 

 the sides of the moimtain. Sometimes the mud-floes are 

 formed on a large scale, and, descending with great 

 rapidity, bury up a whole town. It was in tliis way that 

 the ancient cities of Herculaneum and Pompeii were 

 buried up by the great Vesuvian eruption of a.d. 79. The 

 Italians give the name lava d' acqun, or water-lava, to 

 flows of this kind, and they are greatly dreaded on account 

 of their very rapid flow. An ordinary lava-stream creeps 

 slowly along, so that people have time to get out of the 

 way ; but in the case of mud-flows there is often no time 

 for escape. 



Into the question of the cause of volcanic phenomena 

 we cannot enter now ; but we shall have more to say in a 

 second pajjer. 



Notices of Boofts. 



The lloney-Bee: Its Natural History, AHaU»iuj, and 

 Physioloriy. By T. W. Cowan, F.L.S., etc. (Iloulston &. 

 Sons.) This little manual, which, though consisting of 

 upwards of 200 pp., is scarcely larger than pocket-size, 

 forms the natural supplement to the author's numerous 



works on Bees and Bee-culture. The subject is handled 

 in an exhaustive and thoroughly scientific manner, and 

 the book, which is written in a cominendably concise style, 

 and contains upwards of seventy figures, teems with 

 rehable information. The labour of compilation must 

 have been great, and the author deserves the thanks, not 

 only of ajsieulturists, but of all who are interested in the 

 anatomy and physiology of insects in general, for having 

 put into such a comiJact and inexpensive form so much of 

 the detailed results of recent scientific research. Authori- 

 ties are constantly cited throughout, and the references to 

 the copious bibliography appended supply the reader with 

 all that is necessary to guide him in pursuing the subject 

 further. Taking a look into a hive at the height of its 

 activity, we are introduced to the queen " mo^dng slowly 

 over the combs, surrounded by a number of workers, 

 which are constantly touching her with their antennte, 

 and offering her food. She stops at an empty cell, 

 examines it by putting her head inside, then, hanging on 

 to the edges of the comb, inserts her abdomen, and 

 deposits at the base of the cell, to which it is attached by 

 a glutinous secretion, a little bluish-white oblong egg." 

 The position of the egg in the cell is altered day by day, 

 till, sloping gradually from the upright, it eventually Ues 

 in a horizontal direction, as shown at A, B, C, in the 



accompanying figure of a brood-comb. Here also are 

 shown the growing grub, the remarkable crater-like open- 

 ings of the royal cells, drone colls at K, and at N cells 

 containing workers, some of which are just nibbling their 

 way out through the cappings of the cells. Mr. Cowan 

 considers that bees generally confine their honey- and 

 pollen-collecting expeditions to within a radius of about 

 two miles from their hives, except when food is scarce, 

 when they will fly as far as four or five miles. By his own 

 observations he has proved that the rate of flight may be 

 at least as much as twelve miles an hour, i.f. for un- 

 weighted bees, the heavily-laden ones returning from a 

 foraging expedition, of course travelling more slowly. 



Great pains have been taken to give a clear exposition 

 of the mechanism and method of action of the sting. 



