JUNE 5, 1902] 
NATURE 
131 
II. 
The photographs here reproduced are those of the volcanic 
dust which fell in Barbados on Wednesday, May 7. The 
circumstances attending the fall have been so graphically de- 
scribed in a letter, dated May 10, from Mr. G. C. Edghill, the 
manager of the sugar plantation on which the dust fell, to its 
owner, Captain Forte, that it seems best to quote parts of the 
letter verbatim. 
of my father’s) that I owe both the letter and the specimen of 
the dust. 
Mr. Edghill writes as follows :— 
** Wednesday morning, May 7, opened normally, the day being 
fine and a steady breeze blowing. Soon after mid-day we began to 
hear deep subterranean explosions, increasing in intensity, some 
single, others in volleys of about five or six. Some of these 
made the earth vibrate like a slight shock of earthquake, and 
they continued for two or three hours. Then a black cloud 
began torise in the direction of St. Vincent, which rose and 
spread towards and around us, although the wind was blowing 
from us towards it. (The italics are mine.) 
** About four o’clock the edge of this cloud began to obscure 
the edge of the sun, and dust began to fall, at first lightly, but 
increasing gradually in volume, and making a noise like a fine 
drizzle. Rapidly then the light grew dim, and the appearances 
were like those of a total eclipse of the sun, but very grand and 
startling—making one feel creepy. At five o’clock it was quite 
dark, and our mill hands had to be lent a lantern to see their 
It is to the kindness of Captain Forte (a friend | 
size of these dark particles is about 0’008 cubic millimetre. 
When thrown into water, about half the powder sinks at once, 
and if the floating particles be examined with a high power, it 
will be seen that they are all buoyed up by air bubbles; on 
violently agitating the dust with the water, the dust sinks, so that 
it does not seem to contain any of the /égh¢er kinds of pumice, 
| which through their extremely porous nature cannot be made to 
sink so easily. 
When the dust is thrown into a solution of density 2°52 (a 
solution of mercuric iodide in potassium iodide), about one-fifth 
of its particles float ; these are larger and lighter in colour than 
the rest, and under the microscope have the appearance of a 
yellowish-brown semi-transparent glassy material, with bubbles 
in it, and numerous fine air tubes running through its substance 
all more or less in one direction; moreover, it shows evident 
signs of fusion on its surface, and is no doubt a rather heavy 
kind of pumice ; along with these particles are some of a clear 
greenish glass, full of cavities whéch do not act on polarised 
“ight—they are transparent obsidian or true volcanic glass. Of 
the particles which sink in the double iodide solution, those of 
black, metallic-looking magnetite have already been mentioned, 
and also the dark-coloured mica ; with these there are remark- 
ably perfect crystals of a felspar, some of which contain cavities 
of a regular geometrical shape. These crystals have curiously re- 
tained in many instances the primitive sharpness of their edges. 
Probably a sodium felspar is present, as well as the potassium 
compound, for the ash, after digestion with pure ammonium 
way home. At six o’clock it was as dark as midnight, and we 
went to bed as usual, the only disturbance in the night being 
incessant thunder and lightning in the direction of the mountain. 
- . . When the daylight came it was alarming to see everything 
covered by a layer of dust a quarter of an inch thick. [ 
Say a quarter of an inch, because I put out a dinner plate on 
the lawn above the house when the fall began, and the next 
morning the dust lay a quarter of an inch thick on it. All the 
freen had given place to a light brown, and the canes had 
almost quite disappeared. . . . 
dust was cool and smelling strongly of brimstone. It is 
estimated that upwards of fifteen tons per acre fell on the 
island... .” 
To turn to the two photographs, which show the dust magnified 
exactly seven and a half diameters (or about 56 times in area). 
Fig. 2 is precisely the same view of the same dust particles as 
those seen in Fig. 1, except that the light comes through them 
in Fig. 2 whereas it is shining down upon them in Fig. 1. In 
other words, Fig. 1 is by reflected light, but Fig. 2 by trans- 
mitted light ; Fig. 2 therefore shows clearly which particles of 
the dust are transparent and which opaque; and it is very 
instructive carefully to compare Figs. t and 2. It will be seen 
at once what a very large proportion of the particles are trans- 
parent—more than two-thirds, in fact. Most of the opaque 
particles are very strongly magnetic, and are certainly magnetic 
oxide of iron (they are not titaniferous iron, still less hematite). 
But these are mixed with others, also attracted by the magnet, 
but far less so, apparently of a dark-coloured mica. The mean 
NO. 1701, VOL. 66] 
| after 
Fic, 2. 
fluoride, leaves a residue giving a brilliant and long-lasting yellow 
colour to a Bunsen flame, and with a spectroscope, the lines of 
potassium and calcium are brilliantly shown as well as the 
double sodium line. There are also in the ash a considerable 
number of splintered crystals, of conchoidal fracture, and hard 
enough to scratch glass, which, like all the crystals present in 
this ash, act powerfully on polarised light ; they are quartz, and 
| the edges of most of these particles are blunt and the corners 
a | visibly rounded. 
I forgot to mention that the | 
There are also a large number of transparent 
crystals of a brownish-green colour, very well preserved in 
form, which a rather hasty examination would indicate as 
olivine, but of this I do not feel quite sure. The residue 
the ammonium fluoride treatment proved to consist 
chiefly of compounds of iron, calcium and magnesium ; there is 
a trace of some metal present which forms a sulphide insoluble 
in hydrochloric acid, but what it is I could not deter- 
mine, the total quantity of ash at my disposal being only 
1°304 grams. Perhaps it is copper—whatever it may be, it is 
only present in very minute quantity. Magnesium is present in 
considerable quantity, almost certainly as a silicate. There is 
more than a trace of manganese, and aluminium is also present, 
but only in very small amount. Barium and strontium com- 
pounds are absent. The dust, when heated carefully in a hard 
glass tube, gives off a trace of water, which it appears to hold 
mechanically, and afterwards yields a slight crystalline sublimate, 
probably of some ammonium compound (? the chloride). No 
sulphur could be certainly detected, in spite of the strong 
sulphurous smell which, it seems from the account, the dust had 
