MEASURING FOG.

Press, Volume LV, Issue 16702, 10 December 1919, Page 6

MEASURING FOG.

HOW IT IS DONE. (.FROM OCR OW.V COItUESrONDENT.) LONDON, October 23. No one likes a London fog. Even thoso born and bred in it gruuiblc, often withont much provocation. New Zealand visitors are frankly nbusive of its nuptaasantness and its often tiresome sequelae as aflccting tho health.

It is interesting to read that during the laot few days a now dovicc for fogrecording has been nt work on top of a high building in Victoria streot, and for tho lirf«t timo a fog has bcon filtered and its diri The inventor of the devico is Dr. J. S. Owens, honorary sooretarv to tho Advisory Committee of the Meteorological Officc on Atmosplioxic Pollution. "For somn time p;ist," he said, "by mnana of K-iup'ts set. np in different parts of the conntrv, we hflv-e been aWc to moofioro tho dirt deposited by fog. In tho year ended March 31 st, ii«chd:de iiad Liio highest figure, with a mean monthly de|»sit of 77.0 tons of dirt por square mile. Wandsworth Common was lowest, with 10.2 tons, tvhilo in tho EmhanKmpJit Gardens the monthly average was 57 tons per Sfjnaro mile. By means of my filter wo can now tell tho amount of this dirt in tho atmosphere. "At its worst, about noon last Sunday," said Dr. Owens, "the weekend fog represented the last bnt one shade on tho 6caJo, which is l-18th grain of dirt per cubic yard. It doesn't sonnd very much, but when ynu hare to breathe it honr after hour it is a mighty lot. A man breather about one cubic yard of air in two hours. A rough analysis of tho dirt shows that in consols of finely divided soot, which contains from -1 to 5 per cent, of sulphur." Here is a description from the '•'Daily Mail" of how thy record is taken:—'

Dr. Owens prodnccd several discs of wliito blotting paper of ahout 6 inch diameter. Tm*o were divided up like tho i'aco of a 24-hour clock, and round their mar pin were many other dines, or blobs, each of J-inch diameter, and of varying shades of prey. Tho latter wero tic actual records of tho wook-end fog, as registered during each hour of the twenty-four. On tho filtering machine one of theso blotting paper discs is placed, and it makes n complete revolution by clock-work in a day and a n ; ght. At the same time by means of water pressure the revolution of tho disc is stopped at intervals, and the margin is gripped tightly between the open ends of two narrow pipes, and two litres of air (about half a gallon) is drawn through the pipes and tho paper, leaving the filtered dirt in the form of a blob of grey, as already mentioned. Thus the colour of the dirt at rach hour 13 discovered. Tho next step is to determine what amount of deposit leaver that exact shade of grey. To do this a chart of different grey shade*, each one numbered, is brought into use. This chart, was devised after careful wcighinc of fog deposits on discs large enough to hold fog dirt in weighable quantity. It was thus discovered exactly what weights were represented by every shade of grey on the chart. Shade one 011 the scale, for instance. represents 1-265 th grain per cubic yard. Thefa are* ton shades altogether, and each small square on which ihev are shown hfis a holo in the ccntre. "By placing the fog record under the scale, it is easy to find out with what shade the darkest blob on the record corresponds, and thus the amount of dirt in the atmosphere.