234 
NATURE 
quakes. As Mr. Brigham states, ‘‘No words can convey an 
idea of its horrible roughness and hardness.” 
My own belief is that ‘‘aa” has been formed simply by 
obstructions breaking the quiet flow of molten lava. Every 
observer has noticed that ‘* pahoehoe” contains ducts and air- 
chambers, having an upper crust contorted into the shape of the 
waves and ripples of the flowing lava. The liquid lava has 
evidently flowed in these ducts and chambers, and at last flowing 
out has left them empty with glazed interior surfaces. In like 
manner torrents of lava have poured through caverns down the 
mountains to the sea, and flowing out have left the innumerable 
caves, smooth and shining within, to be found all over the 
island. Now, when there are obstructions on the earth’s surface 
or meeting flows, this system of ducts is broken up, and frag- 
ments of lava are carried along on the surface, piling up higher 
than the adjacent ‘‘ pahoehoe,” like ice-packs in rivers, and 
sometimes rolling immense boulders twenty and thirty feet high, 
which now stand on the ‘‘aa” with the drip glistening over 
them. This theory is confirmed by the fact that ‘‘ aa” is always 
higher than the adjoining ‘‘pahoehoe,” and also by the fact, 
which I especially noticed in the flow of 1859, that wherever 
there are open spaces in lava flows (kipukas), the old lava under 
the flow is found to be ‘‘ pahoehoe” under ‘‘ pahoehoe”’ and 
aa” under “‘aa.” 
While surveying the region I was extremely interested in the 
arrangement of the craters ; and now having determined the 
situation of more than fifty of them on Mauna Loa, Hualalai, 
and Mauna Kea, I have ascertained that there is a method in 
their arrangement. They are not arranged relatively to the 
mountain on which they are situated, but relatively to the points 
of the compass. There seems to have been a series of nearly 
parallel fissures through which these craters have risen, in lines 
running from S. 40° E. to S, 60° E. There are a few arranged 
in lines running N. 50° E. 
It has been remarked by Mr. W. T. Brigham that, while the 
general trend of the Hawaiian group and of the major axis 
of each island is N. 60° W., there is no crater on the islands 
whose major axis is parallel to this line. ‘‘On the contrary,” 
he continues, ‘‘a very interesting parallelism is observed among 
all the craters, and invariably the longest diameter is north and 
south.” It would be more correct to say that the major axes of 
the great craters are generally at right angles to the general axis 
of the group, 7.e. about N. 30° E. Haleakala and the ancient 
Kipahulu caldera appear to take the other direction, but the 
statement is certainly true of the great calderas of Kilauea and 
Mokuaweoweo, which have other points of resemblance. 
Thus in both the highest walls are on the western side, and in 
both the action is working towards the south-west, as is indicated 
by the fact that the north-east craters are nearly filled up, while 
the deepest and active craters are in the south-west end of the 
caldera. 
It has been shown by Prof. Dana and other geologists that 
the principal mountain-ranges of the globe, as well as the main 
coast-lines and chains of islands, take the two directions just 
mentioned, “which are in general tangential to the Arctic and 
Antarctic circles.” Thus it appears that the laws in accordance 
with which the volcanic forces are now operating in these islands 
are the same as those by which all the grand features of our 
world have been established, and possibly related to the laws of 
crystallisation which pervade the mineral kingdom ; and thus we 
perceive a unity in the processes of the globe. 
In conclusion, I would remark that to my mind the most 
plausible theory to account for volcanic action is that of Mallet, 
that the contraction of the earth’s crust continually going on 
under the power of gravitation causes as much internal heat as 
would be required to cause a similar expansion. Prof. Dana 
has remarked that ‘‘the fact is well established that motion in 
the earth’s rocks has been a powerful source of heat,”’ and that 
the annual crushing of not over one-sixth of a cubic mile of 
rocks in the earth would cause all the voleanic phenomena of the 
world. This theory has the beauty of attributing all these 
phenomena to a single cause, and of thus suggesting the thought 
of the one great Power above the inexplicable forces of 
gravitation, who continues all the forces of the universe. 
IMMISCH’?S THERMOMETER 
“HIS instrument depends for its action upon the opening 
and closing of a minute volute Bourdon tube, which for this 
purpose is filled with expansive liquid and hermetically sealed. 
[xaly 8, 1886. 
One end of the tube is fixed, and the free end is brought into 
contact with the short arm of a lever, the long arm of which 
forms a rack gearing with a pinion which carries the pointer. 
The position of the tube with regard to the short lever-arm is 
such that for ordinary purposes the divisions on the dial are 
equal, while for clinical use the scale is an increasing one, in 
order that near blood-heat the divisions become wider to permi 
of a fraction of a degree being read off accurately. 
The success which these instruments meet with is owing prin- 
cipally to their sensitiveness, accuracy, and non-liability to get 
broken, If they should meet with an accident they can be easily 
repaired. 
The appellation “‘ metallic” does not seem to be a happy one 
for these thermometers, as they are likely to be confounded with 
the unsuccessful attempts which have been made to produce 
instruments for similar purposes by means of bi-metallic lamina. 
The defects of the latter are the extremely small v/s vzva ayail- 
& 
— 
4 
able for the work of multiplying the small motion of the laminze, — 
and the liability to not return to precisely the same point after 
being subjected to extremes of temperature. In this latter 
respect there is a double security with the instrument which is — 
the subject of this notice. The tube is in itself a very flexible 
spring, the motion of which does not overreach the limits of | 
perfect elasticity, and its position at any given time is deter-_ 
mined by the volume of the liquid, which, of course, remains — 
always a constant quantity whatever the volume may be. As 
the tube is absolutely full, it must of necessity always accommo- 
date itself to the volume and correctly indicate the temperature. 
As regards accuracy, we are informed that upwards of 500 
have already been tested at Kew—we have ourselves seen the 
certificates of the last group of two dozen clinical ones, and ~ 
they give the remarkable results of perfect accuracy at 66 per 
cent. of the points tested, and of no error greater than 0°°2 at 
any point on any one of the twenty-four thermometers. Al 
‘ 
SCIENTIFIC SERIALS j 
Rendiconti del Reale Istituto Lombardo, May 13.—On the 
theory of waves, by Prof. E. Beltrami. The author presents 
some considerations which place ina clearer light the process 
by which F. Neumann deduces the laws of Fresnel from the 
fundamental equations of elasticity.—Dynamics of moving sys- 
tems which preserve their mutual affinity, by Prof. C, F ormenti. 
Rivista Scientifico-Industriale, May 31.—Maximum and rela- 
tive humidity of the atmosphere, by Prof. Paolo Cantoni. 
Hygrometric tables of mean annual moisture, recorded at thirty 
meteorological stations in various parts of Italy, show that the 
average of maximum and relative humidity increases from north 
to south, from elevated to low-lying stations, and from inland to 
maritime districts.—On the persistence of the mathematical 
figure of the earth throughout the geological epochs, and on the 
constitution of the terrestrial crust, by Prof. Annibale Ricco. A 
summary is given of M. H. Faye’s views on this subject already 
published in the Comptes vendus of the French Academy (March 
22 and April 5, 1886), the author concluding that the mathe-_ 
matical figure of the globe, as represented by the surface o} 
oceans, has not been perceptibly modified by the geological 
forces associated with the cooling process. —On the permanent 
magnetism of steel at various temperatures, by Prof. Poloni. It _ 
is shown that at the temperature of 180° C. the well-known law 
of magnetic distribution in steel bars no longer holds good when 
Nenana cee a ae 
