232 
NATURE 
} 
[xuly 8, 1886 
boilers of the Cornish and Lancashire types, and as, with gas, 
we have a fuel which renders every assistance to the experi- 
menter, it will not take long to prove the comparative results 
obtained by the two different forms of web. Those of you who 
have steam-boilers will, no doubt, know the great liability to 
cracking at the rivet-holes in those parts where the pilates are 
double. ‘This cracking, so far as my own limited experience 
goes, being usually, if not always, on the fire side, where the 
end of the plate is not in direct, contact with the water—where 
it is, in fact, under the conditions of one of the proposed webs 
—I think we may safely come to the conclusion that this crack- 
ing is caused by the great comparative expansion and contrac- 
tion of the edge of the plate in contact with the fire ; and it will 
probably be found that if the plates are covered with webs the 
whole of the surface of the plates will be kept at a higher and 
more uniform temperature, and the tendency to cracks at the 
rivet-holes will be reduced. ‘This is a question not entirely of 
theory, but needs to be tested in actual practice. 
There is another point of importance in boilers of the loco- 
motive class, and those in which a very high temperature is kept 
in the fire-box, and this is the necessity of determining by direct 
experiment the speed with which heat can safely be conducted 
to the water without causing the evolution of steam to be so 
rapid as to prevent the water remaining in contact with the 
plates, and also whether the steam will or will not carry mech- 
anically with it so much water as to make it objectionably 
wet, and cause priming and loss of work by water being carried 
into the cylinders, I have observed in the open boilers I use 
that when sufficient heat is applied to evaporate 1 cubic foot of 
water per hour from 1 square foot of boiler surface, the bulk of 
the water in the vessel is about doubled, and that the water 
holds permanently in suspension a bulk of steam equal to itself. 
I have, as yet, not had sufficient experience to say anything posi- 
tively as to the formation or adhesion of scale on such surfaces 
as I refer to, but the whole of my experimental boilers have up 
to the present remained bright and clean on the water surface, 
being distinetly cleaner than the boiler used with ordinary flat 
surfaces. Itis, I believe, generally acknowledged that quick heat- 
ing and rapid circulation prevents to some ,extent the formation 
af hard scale, and this is in perfect accord with the results of 
my experiments. The experiments which I have shown you I 
think demonstrate beyond all question that the steaming-power 
of boilers in limited spaces, such as our sea-going ships, can be 
greatly increased ; and when we consider how valuable space is 
on board ship, the matter is one worthy of serious study and ex- 
periment. It may be well to mention that some applications of 
this theory are already patented. 
I will now show you as a matter of interest in the application 
of coal gas as a fuel how quickly a small quantity of water can 
be boiled by a kettle constructed on the principle I have de- 
scribed, and to make the experiment a practical one I will use a 
heavy and strongly-made copper kettle which weighs 64 lbs., 
and will hold when full one gallon, In this kettle I will boil a 
pint of water, and, as you see, rapid boiling takes place in 50 
seconds. The same result could be attained in a light and 
specially-made kettle in 30 seconds, but the experiment would 
not be a fair practical one, as the vessel used would not be fit 
for hard daily service, and I have therefore limited myself to 
what can be done in actual daily work rather than laboratory 
results, which, however interesting they may be, would not be a 
fair example of the apparatus in actual use at present. 
THE CRATERS OF MOKUAWEOWEO, ON 
MAUNA LOA? 
URING last year I was engaged for many months in survey- 
ing lands on Mauna Hualalai and Mauna Loa, in Hawaii, 
and in that way had an opportunity of making investigations of 
craters and lava flows that may be of interest to those studying 
volcanic phenomena. ae 
It would seem that, as the best histories are those written long 
after the events which they record, when all the reports of eye- 
witnesses can be carefully examined, so the best descriptions of 
volcanic action may be obtained long after eruptions, by carefully 
investigating the records indeliby inscribed in the rocks. 
The ascent of Mauna Loa is so seldom made that a brief 
account of my excursions may be interesting. 
* By J. M. Alexander, from the Yawaiian Commercial Advertiser of 
October 1885. 
On September 1, 1885, I set out in company with Mr. J. Ss. 
Emerson, of the Hawaiian Government Survey, to ascend that 
mountain from the table-land east of Hualalai, along the south 
side of the lava-flow of 1859, which, as many will remember, 
was visited by a party from Oahu College. We were provided 
with mules for riding and pack-donkeys, and accompanied by 
several natives, including a so-called guide, who lost himself and 
delayed us over a day in searching for him, 
Our route led first through a narrow belt of forest, consisting 
of mamane, ohia, and sandalwood trees ; then through a scanty 
vegetation of ohelos and the beautiful Cyathodes Tameiamete, 
and at last beyond the limits of vegetation, without a vestige 
even of moss or lichen, over a wonderful and awful billowy 
waste of ‘pahoehoe” Java, traversed by tracts of ‘faa” and 
deep chasms. ; 
At about two-thirds of the distance towards the summit we 
passed the rugged crater hill from which the outbreak of 1859 
had issued, and here our path was strewed with pumice ane 
“*Pele’s hair” from that eruption. There was an enormous 
quantity of lava poured forth from the small fissure of this” 
crater, forming a stream from half a mile to two miles wide, and 
reaching nearly thirty miles to the ocean at Kiholo. Lower 
down I counted eighteen species of ferns and a dozen kinds of 
phenogamous plants already growing on this flow. In this 
vicinity the caverns contained many carcasses of wild goats. In 
one further south I counted eighty of their skeletons and decaying 
bodies. ‘They had probably leaped in for shelter, and had been 
unable to leap out. 
When near the summit our guide warned us to descend, be- 
cause of an approaching storm; but Mr. Emerson and ue 
anxious to accomplish the object of our journey, set out without 
him through the driving rain that soon turned into hail and then 
into snow, marking our route with flags so that we might be able. 
to find our way back. Ina short time we reached the brink of 
the vast crater of Mokuaweoweo, filled with fog and surrounded’ 
by frightful precipices. Along this brink were numerous deep: 
fissures filled with ice and water, the beginning of cleavage for 
avalanches into the crater. Here, and for a quarter of a mile 
below, we observed many rocks of a different kind from the 
surface lavas, solid, flinty fragments of the foundation walls, 
weighing from fifty pounds to a ton, which had formerly fallen” 
down upon the crater floor and had afterwards been hurled out 
during eruptions. I noticed similar rocks around the summit 
craters of Hualalai. It would be unsafe to approach the crate! 
at this place during eruptions, when such brickbats were 
flying. i 
We returned to our camp about noon, and sent the poor 
animals, which had stood all nigh®in the icy wind tied to jagged” 
rocks, in the care of the guide down the mountain ; and with the 
help of one native, with much difficulty, carried a tent and 
supplies to the summit. 4 
At evening the fog lifted and gave us a glimpse of the craters. 
Immediately below us lay the central crater, surrounded by al- 
most perpendicular walls, with a pahoehoe floor streaked with 
grey sulphur cracks, from hundreds of which there issued 
columns of steam, and with a still smoking cone in the south | 
end, Beyond this central crater on the south rose a high mening | 
and beyond this plateau still further south we saw an openin, 
into another crater small and deep. In the opposite direction, — 
north of the central crater, appeared another higher crater lik 
an upper plateau, from which a torrent of lava had once poure 
into the central crater, and north of this again another crate 
like a still higher plateau, from which also lava had flowed 
south. ‘ 
Thus it was evident, as appeared more clearly by subsequent 
investigation, that Mokuaweoweo is not simply one crater, but @ 
series of four or five craters, the walls of which have broken 
down, so that they have flowed into each other. 
The crater of Haleakala, on Maui, was probably formed in a 
similar manner out of several ancient craters which have broken 
into each other. ‘These vast chasms may well be called calde: 
as has been recommended by Captain Dutton. On Huala 
there is a series of craters having the same relative position — 
those of Mokuaweoweo, and crowded so close together as to b 
almost broken into one. On the older mountains, like that ol 
West Maui, such congeries of craters have evidently formed the 
starting-points for deep valleys, which the rain torrents, leapin, 
down their lofty walls, have torn out through concentric layers 
of lava to the sea. Just before sunset we saw the splend 
phenomenon of the ‘Spectre of the Brocken” (Hookuaka), 
