1890-91.] Mr J. Y. Buchanan on Sulphur in Marine Muds. 39 
approximate numerical result or estimate of the work of earth- 
worms which is interesting. At page 258 he says : “ Nor should 
we forget, in considering the power which worms exert in tritur- 
ating particles of rock, that there is good evidence that on each acre 
of land which is sufficiently damp and not too sandy, gravelly, or 
rocky for worms to inhabit, a weight of more than 10 tons of 
earth annually passes through their bodies and is brought to tho 
surface.” 
On a Simple Pocket Dust-Counter. 
By John Aitken, Esq. 
(With a Plate.) 
(Read December 1, 1890.) 
It is now a year and a half since I communicated to this Society 
a description of a portable form of apparatus for enabling us to 
count the number of particles of dust in the atmosphere. The 
working of that instrument in my hands has been most satisfactory, 
and though it has occasionally given trouble, yet it has not given 
more than might have been expected. Though that apparatus has 
worked quite pleasantly with me, and enabled a beginning to be 
made of an investigation into the amount, and the effects, of dust 
in our atmosphere, yet very few have as yet followed up this line of 
inquiry. This has probably been owing to there being something 
in the complicated nature of the apparatus which has deterred 
others from joining in the work. I therefore determined to see if a 
simpler, and at the same time a reliable, form of the apparatus 
could not he devised. 
After the experience gained in making thousands of observations 
with the portable apparatus, I have acquired an acquaintance with 
its weak points, and a knowledge of what it would be necessary for 
an instrument of this kind to do under the different conditions 
in which it would he required to work, and I may now sum up the 
indictment against the portable apparatus under the following 
heads : — It is too complicated ; it has too many weak points ; it is 
too heavy; it has an unnecessarily wide range for meteorological 
work ; and it is too expensive. If an instrument could he con- 
