396 TRANSACTIONS OF SECTION A. 
Russell for the Meteorological Office some years ago, and appeared to give good 
results. It requires considerable technical skill and has inherent difficulties, 
such as moisture in the wool; it is doubtful if it would give sound results, 
except perhaps in very impure air, as during a smoke fog. It also requires 
elaborate apparatus. The method is described by G. W. J. Russell in ‘The 
Monthly Weather Report,’ 1884 and 1885, by Cohen in ‘J.S.C.I.,’ 1887, and by 
F. Clowes in ‘ J.8.C.1.,’ 1903. 
2. All rain or other deposit falling on a gauge of known area may be 
collected, evaporated, and the residue weighed and analysed. This method was 
used in the investigations made by ‘The Lancet’ about two years ago to get 
the soot fall of London. It does not, strictly speaking, give the amount of 
air impurity, but the amount which falls on a given area (a) in rain, snow, &c. ; 
(6) during dry weather; (a) and () are not separated but estimated together. 
The apparatus used may be very simple, and it is now adopted by the Com- 
mittee for the Investigation of Atmospheric Pollution. 
3. Aitken’s Dust Counter. This is an instrument devised by Mr. John 
Aitken for counting the number of dust particles in air. It is described in 
‘Trans. R.S.E.,’ Vols. XXX. to XXXVI. No attempt is made to obtain the 
composition of the dust particles. 
4, Glass plates may be exposed to the air for a certain time, then washed 
in water and their opacity measured. This method was devised by Professor 
Cohen and used in Leeds. It appears to be useful only for catching matter 
which will stick to a glass plate, e.g., tarry soot. It would seem also that the 
indication given must be affected by the amount of tar present in the smoke 
of a city; 7.e. if there is not sufficient tar present to make the deposit stick the 
indication will be too low. It aims only at comparative results. 
5. A jet of air may be caused to strike a glass plate coated by some sticky 
substance, and the opacity measured. This method may be used either :— 
(a) By causing the air jet to play on the glass for a fixed time and then 
ineasuring the increased opacity by comparison with a calibrated scale; or 
(b) the jet may be made to play for such time as will cause a definite opacity 
and the time required compared with a calibrated time scale. This method is 
suggested for discussion and has not been used. 
6. A measured volume of air may be drawn through filter paper and the 
degree of discoloration produced on the paper measured or compared with 
calibrated papers. This method has been tried in Glasgow with considerable 
success, but it would seem to give results which depend somewhat on the colour 
of the matter caught as well as its amount. 
7. An optical method might be used by which the opacity, to a standard 
light, of a column of air of given length is measured. This could probably 
be arranged to give the quantitative amount of impurity present by preparing 
a scale of opacity from measurements taken on air with known amounts of 
suspended matter present. 
8. Rain might be caught and its opacity compared with a standard scale 
made by adding definite quantities of soot to distilled water. This method, 
or a somewhat similar one, was used by Dr. Fritzsch for measuring smoke in 
chimneys. (See Donkin in ‘ Engineer,’ May 26, 1899.) The method is open 
1o the same objection as No. 2, also its results would depend on the nature of 
the impurity as well as the quantity present. 
9. Boxes may be exposed having a collecting surface of one square foot and 
the contents collected and analysed. Such boxes were devised by Mr. Peter 
Fyfe, Chief Sanitary Officer, Glasgow, and exposed in that city in prominent 
positions. The method is a simplified form of No. 2. 
7. Temperature Frequency Curves. 
By E. Goup, M.A., and F. J. Wurppiez, M.A. 
8. The Lunar Influence on Terrestrial Magnetism, and its Dependence 
on Solar Periodicity. By SypNny Cuapman, D.Sc. 
