ae 
410 
month’s computation of the tides of Boston 
harbor, the differences in the heights rarely ex- 
ceeded more than 0.1 of a foot, and in the times 
more than three or four minutes. These dif- 
ferences arose from a slight yielding of some 
parts of the machine from a lack of sufficient 
rigidity. This, however, could be mostly 
remedied at small expense, if thought neces- 
sary, by making some parts of it a little more 
rigid. 
In a comparison of the results given by the 
machine for three months, of the tides of San 
Diego, Cal., having very large diurnal com- 
ponents, with the times and heights from ob- 
servation, the average of the differences, taken 
without regard to signs, was 0.29 of a foot, and 
in the times about ten minutes. But these 
differences are due mostly to meteorological 
causes, changes in the winds and in the baro- 
metric pressure, which cause fluctuations in 
the mean level of the sea, and are due only in 
a small measure to imperfections of the ma- 
chine. ‘These are most conspicuous in cases 
where the tide-wave becomes very flat from the 
high or low water of any day being brought 
very nearly to mean sea-level from the effect 
of large diurnal components, or where the 
whole range of the tide is very small; but in 
such cases the times of maxima and minima 
are very indefinite, and the error is more in 
appearance than in reality. 
The machine is now being used in the pre- 
diction of the tides for the tide-tables of the 
year 1885, and is in all cases first applied for 
each station to some year for which there are 
observations for comparison, and, with the 
exception of the slight defect referred to, is 
giving entire satisfaction. The capacity of the 
machine for doing work is at least that of thir- 
ty to forty computers, if these were to take into 
account every thing which the machine does. 
In fact, little more time is required than that 
which is taken up in recording the results. 
NOTES ON THE LAVA-FLOW OF 1880-81 
FROM MAUNA LOA. 
THe Hawaiian Islands are entirely of vol- 
canic origin. The various islands appear very 
distinctly to be of different ages, the volcanic 
agencies still being continually active in the 
most south-easterly one, while in those to the 
north-west they have been extinct for a long 
period of time. 
Hawaii, the largest island, situated at the 
extreme south-west of the group, has an area 
of about 4,200 square miles, being about twice 
the size of the state of Delaware, and not quite 
SCIENCE. 
[Vor. IIL, No. 61. 
so large as Connecticut. 
nent elevations, each of which marks what is 
or has been a centre of activity. The Kohala 
Mountains, with an elevation of about five 
thousand feet, form the northern end of the 
island: though thickly covered with well pre- 
served crater-cones, their activity ceased before 
the earliest traditions of the natives. Mauna 
Kea, the highest peak of the group, with an al- 
titude of 13,825 feet, has also long been ex- 
tinct. This lies to the south-east of the Kohala 
Mountains, on the eastern coast. Nearly op- 
posite, on the western coast, is Mauna Huala- 
lai, a little more than 8,000 feet in height. ‘The 
last recorded eruption from this took place in 
the year 1801. When visited in the spring of 
1882 by J. T. Perryman and J. S. Emerson 
of the Hawaiian government survey, steam was 
found to be issuing from several of the fissures 
on the summit. 
South of the preceding three elevations is 
Mauna Loa, on whose summit, 13,610 feet 
above the sea, is the active crater of Moku- 
weoweo. ‘The slopes of Mauna Loa are very 
gentle, and, when seen from a distance, the 
whole mountain appears like a gentle swell of 
land. On its eastern slope, at an elevation of 
about 4,000 feet, is the famous active crater 
of Kilauea. This is commonly regarded as a 
portion of the mountain of Mauna Loa; but it 
is in reality a separate mountain, though situ- 
ated so near the other that the lavas from each 
have flowed together till the outline of this 
mountain has nearly been merged in that of 
the other. As seen from the upper portions 
of Mauna Loa, the individuality of Kilauea is 
clearly apparent. 
During the last hundred years many flows of 
lava have taken place from both these moun- 
tains ; all bursting forth from the sides approx- 
imately near the summit, but none coming from 
the crater itself. These have been well de- 
scribed by Rev. Mr. Coan of Hilo, Hawaii, by 
W. T. Brigham of Boston, and others. 
On the 6th of November, 1880, the latest 
of these flows burst from the north-eastern 
side of Mauna Loa, at an altitude of about 
10,000 feet. From this point it gradually 
passed down the slope of the mountain, at 
first toward the north-east; then, making a 
sharp bend, it flowed for some distance toward 
the south-east, and then, once more making a 
sharp bend, took a course directly toward Hilo, 
a small but pretty village on the eastern coast. 
The first portion of its course was over a coun- 
try composed entirely of naked lava above the 
limits of vegetation. It then entered the belt 
of forest which skirts the mountain with a 
It has four promi- ‘= 
