October 14, 1909] 



NA JURE 



469 



of three miles north-east of the town. The waste of fuel 

 in the form of unburnt coal passing into the atmosphere 

 is represented each year by about 300 tons per square mile 

 in the centre of the town, or, over the whole area of 

 four miles square, about 100 tons per square mile. The 

 effect of these suspended impurities in diminishing the 

 amount of sunlight in Leeds may be gathered from the 

 fact that in 1907 the number of hours of bright simshine 

 was 1 167 in the town, whilst four miles north-west it 

 reached 1402 hours. The amount of daylight has also 

 been recorded at two different periods by the quantity of 

 iodine liberated from an acid solution of potassium iodide. 

 On the first occasion, over a period of four winter months, 

 it was shown that the smoke in an industrial centre 

 absorbed one-quarter of the daylight as compared with a 

 station one mile to the north-west. In the present in- 

 vestigation, carried out during the month of June of this 

 year, the amount of daylight often fell to one-half in the 

 centre of the town as compared with Garforth several 

 miles away. The relation of soot deposit (black column) 

 to daylight (light column) is shown in the diagram 

 (Fig. 2). 



It is the tarry matter in the soot which causes the latter 

 to adhere to and blacken buildings and vegetation. It is 

 sometimes stated that it is the domestic smoke rather than 

 industrial smoke which is injurious to plant life, on 



2.HUNSLET 

 S.BEESrON HIIJ 

 4.PH(LOSOPHICAI 

 S.HCADINGl.EV 

 7 OBSfZRVAIORY 



9. weerwooD lainii 

 s 



HAI,L 



•15 7 1) 



Fir.. 2. — Influence of Suspendtd Matter on Intensity 



account of its higher content of tar. There is a certain 

 justification for this statement, for the percentage of tarry 

 matter in the total solid impurities is highest in the resi- 

 dential and lowest in the industrial areas, varying from 

 18 per cent, in the former to 4 per cent, in the latter. 

 When, however, account is taken of the total tarry matter 

 deposited each year, the industrial centres are responsible 

 tor the greater quantity, which reaches in some cases ten 

 times the amount in the residential districts. The total 

 ■julphur, either as sulphurous or sulphuric acid, is every- 

 where high, but particularly in and near the chief manu- 

 facturing areas. .\. large portion of the free acids is 

 neutralised either by the alkaline fumes of the blast 

 furnaces or by the ammonia of the burnt coal. Still, free 

 acid is present in considerable quantity, and In Hunslet 

 (industrial centre) represents an annual deposit of 90 lb. 

 per acre, or 25-30 tons per square mile. 



It Is the sulphurous acid which imparts to town fog Its 

 choky and Irritating effects. The large amount of this 

 acid present in fogs may be gauged from the fact that 

 the hoar-frost collected during the dense fog of January 27 

 contained acid corresponding to 10.29 parts per 100,000, 

 or more than ten times the average acidity of the same 

 station. 



To demonstrate the detrimental effect of sulphuric acid 



NO. 2085, VOL. 81] 



upon vegetation, Timothy grass was sown on May 12, 

 190S, in bo.xes i foot square, the soil being uniform. The 

 seed was watered at a rate corresponding to the average 

 rainfall of 25 inches with water containing different 

 amounts of sulphuric acid. In addition to this, three 

 other samples were watered with Garforth rain water in 

 which the acidity was neutralised, the second with ordinary 

 Garforth rain water, and the third with Leeds rain water. 

 The results were very instructive. In the case of Leeds 

 rain water and of those waters containing a higher degree 

 of acidity, germination was distinctly checked, and the 

 delicate green of the young grass quickly changed to 

 yellow or brown. Grasses watered with water containing 

 32 parts per 100,000 were killed In a little more than 

 three months, and with 16 parts per 100,000 in less than 

 a year. 



Chlorides are found in large quantities, especially in the 

 industrial centres, where, expressed as common salt, they 

 sometimes reach as much as 3 or 4 cwt. per acre, a 

 quantity which must be distinctly prejudicial to vegetation. 



The nitrogenous Iinpurlties, on the other hand, would 

 be beneficial by acting either as direct stimulants and 

 fertilisers or by neutralising the acidity of the sulphur and 

 chlorine compounds. 



.1/.4 TH£M.4T/CS A'ND PHYSICS AT THE 

 BRITISH ASSOCIATION. 



T^HE proceedings of Section A began on Thursday, 

 ■^ .August 26, with the address of its president, Prof. 

 E. Rutherford, F.R.S., which has already been printed in 

 full in these columns (Nature, August 26, p. 257). 



A paper followed, by Prof. J. H. Poynting and Mr. 

 Guy Barlow, on the pressure of radiation against the 

 source. The authors employ thin slips of material which 

 become heated by incident radiation. Those black on 

 both sides experience a pressure equal to the energy- 

 density, P, of the Incident radiation ; those black on the 

 incident side and brightly silvered on the other experience 

 a pressure 1-67 times as great, the excess being due to 

 the radiation which is emitted by one side only of the 

 plate. Plates which are bright both sides experience a 

 pressure 2P, because they do not become heated. Experi- 

 ments, which are in progress, give good accord with theory. 

 In a short discussion which followed. Prof. Hull intimated 

 that he was alive to the possibility of this reaction when 

 making his experiments on the pressure of incident radia- 

 tion, but his experiments had been devised carefully so as 

 to prevent its occurrence. 



Prof. T. Lvman then gave a summary of the ascertained 

 properties of light of very short wave-lengths (" .Schumann 

 rays "), including their ionising and photoelectric effects. 

 To these Prof. Bumstead added that one of his students 

 had shown that the velocltv of the electrons emitted photo- 

 electrically increases directly as the frequency of the light 

 up to a wave-length A = 1250 — a result which Ladenburg 

 had previously shown to hold good for ordinary light. 



Prof. Percival Lowell followed with an account of the 

 photographs of Jupiter taken at the Lowell Observatory. 

 The slides exhibited showed a wonderful amount of detail, 

 the most noteworthy features being faint wisps that criss- 

 cross the several belts, particularly the bright equatorial 

 one. He explained the belts and wisps as gaps in the 

 clouds formed bv condensing of uprising vapours from 

 Jupiter's heated interior (he being still a semi-sun), and 

 strung out by his rotation. Prof. Larmor added greatly to 

 the interest of ■ the paoer by exhibiting some early draw- 

 ings of Jupiter made by Sir W. Huggins. and stated that 

 Sir William's opinion from the first was that the wisps 

 wore the edges of cumulus clouds. He noted that the high 

 albedo of Juoiter (72) indicates that the Jovian atmosphere 

 acts like a bright cloud ; It follows that very little of the 

 meteorologv of Jupiter can be due to the sun if heat ii 

 onlv absorbed like light. Other planets with a low albedo 

 would have surface markings more like terrestrial ones. 

 The day's proceedings concluded with a paper, by Prof. 

 E. E. Barnard fread by Prof. E. W. Brown), on the- 

 motion of some of the small stars in Alessier 92 (Herculis). 

 Two of the stars in this cluster are shown to have proper 

 motion; the first (No. 11 of Schultz's list) is moving awa" 



