JUNE 2), 1884.] 
where it attained depths of from 20 to 40 
metres ; rising even to 60 or 80 metres on the 
flanks of Rakata (corrupted to Krakatau), the 
southern and highest part (822 metres) of 
the island. Fragments the size of a fist were 
thrown 40 kilometres from the volcano. Be- 
tween Krakatoa and Sebesi, to the north, the 
ashes and pumice filled the sea at two points, 
forming low islands (Steers and Calmeijer), 
which have already been much broken and 
degraded by the waves. ‘The sixteen little 
craters reported near where these islands stand 
have had no existence: they were only smoking 
heaps of ashes. 
The precise hours of the heaviest explosions 
were not determined directly, but were based 
on the self-registering pressure-gauge of the 
gasometer in Batavia, as there was no self- 
registering barometer there. Making seven 
minutes allowance for the time of air-wave 
passage from the volcano to the gauge, the most 
violent eruptive action occurred at 5.35, 6.50, 
10.5 (maximum), 10.55 a.m., Aug. 27, Batavia 
time. It was these air-shocks that were felt 
by barometers all around the world. In the 
May eruption, sounds were heard 230 to 270 
Inlometres ; but in August the noise of the ex- 
plosions was audible 3,300 kilometres from the 
island, or within a circle of 30° radius, equal- 
ling one-fifteenth of the earth’s surface. The 
sounds spread irregularly ; and it is suggested 
that the wind and the ashes in the air had 
much to do with the silence at points near 
which the eruption was distinctly heard. The 
eruption of Tomboro in 1815 was heard only 
half this distance; but the quantity of its 
ejected material (calculated from a correction 
of Junghuhn’s data) was eight to eleven fold 
that thrown from Krakatau, which Verbeek 
determines to be close to 18 cubic kilometres. 
Two-thirds of this fell within 15 kilometres of 
its origin, as will be shown on an ashes-map, 
to be published in the final report. ‘The ashes 
contain from sixty to seventy per cent of silica. 
Under the microscope, they show, 1°, glass in 
small, porous, irregular fragments; 2°, plagio- 
clase felspar, with inclusions of glass, apatite, 
augite, and magnetite ; 3°, pyroxene, probably 
rhombic as well as monoclinal, with inclusions 
of glass, apatite, and magnetite; 4°, mag- 
netite in grains and octahedrons; this is the 
oldest component, and decreases in quantity 
on receding from the island. ‘The great ten- 
o’ clock wave, which it is thought resulted from 
the falling-in of the northern part of the island, 
following the most violent explosion, rose to 
heights of 30 and 35 metres on some of the 
neighboring coasts, and destroyed more than 
SCIENCE. 
765 
thirty-five thousand people. Maps, tables, 
and drawings are in preparation for a more 
detailed report; and this, in connection with 
the report we may expect from the sun-set 
committee of the Royal society, will form a 
most entertaining addition to the already in- 
teresting literature of volcanoes. 
STOKES’S LECTURES ON LIGHT. 
Burnett lectures on light. First course, on the nature 
of light. By GrorcGr GABRIEL SToKEs. Lon- 
don, Macmillan, 1884. 9+133 p. 24°. 
Tuis little book consists of lectures delivered 
at Aberdeen in November, 1883. They have 
their origin in an interesting manner, which is, 
perhaps, possible only in Great Britain. Just 
a century ago John Burnett, a merchant of 
Aberdeen, bequeathed a fund to establish 
prizes for theological essays. These prizes, a 
first and second, were to be competed for once 
in forty years; and awards have been made 
on two occasions since the foundation. In 
1881, however, a new direction to the foun- 
dation was given by order of the secretary of 
state for the home department, in which it was 
provided that a lecturer should be appointed 
at intervals of five years, to hold office for three 
years. The subjects to be treated are, 1°, his- 
tory ; 2°, archeology ; 3°, physical science ; 4°, 
natural science. Professor Stokes was chosen 
as the first lecturer. 
The lectures are unique, as far as our knowl- 
edge extends, in the effort to present the higher 
portions of optics without the employment of 
experimental demonstrations, diagrams, or 
mathematical language. 
Whether the knowledge assumed in the 
reader, which does not include any thing of 
the theory or phenomena of interference, dif- 
fraction, double refraction, or polarization, is 
sufficient to enable him to understand every 
thing contained in the lectures, is problemati- 
cal. But, at any rate, to those better equipped, 
the book gives a most concise and interesting 
review of the history of optics. A personal 
reminiscence of a conversation with Sir David 
Brewster (p. 15), the last great champion of 
the theory of emission, just after his return 
from Paris, where he had witnessed Foucault’s 
crucial experiment regarding the velocity of 
light in air and in water, is highly interesting ; 
for it shows us the singular motive which pre- 
vented even so acute a mind as Brewster’s 
from yielding to overwhelming evidence: ‘‘ he 
was staggered by the idea, in limine, of filling 
space with some substance merely in order 
