126 



NATURE 



( ) ( 1 1 1 1 ; i i 17. 1 1 ) I 8 



itet bn adth, is additionally w eakened 

 by the 1 ' J t-6i, we obtain I 1 S 375 F01 a n iugh 

 estimate oi the relative brightness without restriction 

 to an) pai licular colour. 

 Sofa 1 have not met with an) published estimates 

 lative In ightness "I thi bov, s 01 "I the pre- 

 cise character of their polarisation, so ili;it these 

 1: ... 1.. oi inten st. Ch vs. T. Win rMEi 1 . 

 [nvermay, Hyde Park. Leeds, October 4. 



An " Arbor Day-" 



At tlv.- meeting of tin- conference "I delegates from 

 provincial scientific societies in the British Association, 

 held on July 4, a resolution was passed establishing 

 October 2 1 as an "Arbor l>a\," and all the delegates 

 present pledged themselves each to plant a trei i! 

 possible cm that day, and to endeavour to induce 

 members of .ill theii societies and others to do the 

 same. The time is now approaching for ibis to be 

 carried into effect, and iliis letter is intended as a 

 reminder. 



By the wholesale cutting down of trees in this 

 country during the last few years the scenerj of our 

 few woodland areas is losing its beauty, and we are 

 greatly entrenching upon our very small reserve of 

 timber. Although it is only In State action that the re- 

 afforestation of our country can be adequately effected, 

 it is hoped that l>\ the carrying out of ibis resolution 



some little benefit may be derived, and that year by 

 war our "Arbor l)a\ " ma} remind us of the paramount 

 necessity of augmi nting our bona supply of timber. 

 John Hopkinson. 

 Weetvvood, Watford, October 14. 



Students' Microscopes on Loan. 

 YVf. are conducting science classes on the lines of 

 communication in France, and it has been suggested 

 to us that some of your readers might care to loan 

 students' microscopes for use in this work. If any 

 who possess sueb instruments care to help us in this 

 way, I shall be glad to hear from them. It will be 

 understood that the instruments will be carefullj 

 kepi and returned intact when finished with. 

 R11 11 u;i> Wilson, 

 Tin Librarian, Red Triangle Library. 

 Wimborne House, Arlington Street, S.W.i. 



THE FUTURE OF THE COM. TRADE. 

 FHE Coal Conservation Committee of the 

 J- Ministry of Reconstruction has recently 

 issued its final report, which forms, it need scarcely 

 be said, a document of first-rate importance. Its 

 form i lecidedly curious, inasmuch as the report 

 in itsell is confined to a hare statement of the 

 action • the Committee in appointing sub- 



ccmmil the general adoption of the reports 



of these mittees, which are printed as 



appendici porl ; these reports are by the 



Power Generation and Transmission Sub-Com- 

 mittee, the 1.1 d sui, -Committee, the Mining 

 Sub-Committee, and the bonisation Sub-Com- 

 mittee. OI ib. inal port of the Mining 

 Sub-Committee is undoubtedly the most interest- 

 ing, and the most valuable in so far as it con- 

 tains a number ol rec mmendations of great 

 technical and economic importance. Indeed, the 

 reference to this sub-commit tec, which instructs 

 "to consider and advise what improvements can 

 ted in the present methods ol mining coal 

 NO. 2555, VOL. I02"! 



with a new in prevent loss ol coal in working ami 



to minimise cOSt ol production," Covers n subject 

 of most vital importance to the entire nation. 

 British industrial .supremacy is built up essentially 

 upon a cheap and abundant coal supply, and vvhen- 

 e\ei thai supply becomes either less than suffii ient 



for British industrial requirements, or more 1 \ 



pensive than that of competing nations, Britain 



will cease to be a lirst-class Power. The safety and 



welfare of the nation thus depend so absolutely 



upon llie coal supply that the recommendations ol 



the Committee charged with its consideratioi 



assume a 1 haracter ol wide national interest. 



The two principal subjects discussed are tin 

 loss anil wasti of coal and the cost of production 



The former is subdivided into waste at the pit- 

 head and loss underground. Waste al the pit- 

 head is essentially confined to the excessiv( 

 amount of coal used for colliery consumption. 

 Relatively complete returns, representing '17 pet 



cent, of the coal output of the country, have been 

 obtained, so that tolerably trustworthy data are 



available, though it may In- readily granted that 

 the collieries that have failed to make returns an 

 those at which the consumption is unduly high. 

 The average colliery consumption for the kingdom 

 is given as 6"8 per cent, of the output, or 

 i.S,4oo,ooo tons of coal; in one of the other 

 reports an estimate is given of the power em- 

 ployed in the mines and quarries of the United 

 Kingdom, which is stated as 4000 million h.p.- 

 ln ins. faking this figure as due to the collieries 

 alone, it would appear that our collieries consume 

 no fewer than 1C3 lb. of coal per h. p. -hour, so 

 that there is obviously room for much improve- 

 ment. The report makes no reference to another 

 source of waste, namely, the "free coal " which 

 i.s allowed to coal-miners in some districts. 

 Everyone who has had experience of these dis- 

 tricts knows that the collier uses his free coal 

 most extravagantly, and that quite considerable 

 economies might be effectid in this item without 

 causing the slightest hardship, or even inconveni- 

 ence, to the men concerned. Loss of coal under- 

 ground is considered as arising from various 

 causes, eai b of which is duly investigated. 



The Committee considers that there has been a 

 substantial improvement in respect of the small 

 coal cast back into the goaf within the last ten 

 years, and estimates the loss due to this cause as 

 o'gi per cent, of the output in 1915. It is obvi- 

 ously difficult to obtain accurate figures on this 

 point, tin collieries that are the worst offenders 

 being, of course, those which furnish no returns, 

 so that it is safe to sav that the figures published 

 by the Committee are below the actual wastage. 



The onlv recommendation made is that a greater 

 demand for small coal should In created for 

 example, by extending the market for briquettes. 

 The present moment, when pitch is unusually 

 cheap and the demand for household coal 

 acute, is peculiarly suited to the generalisation 

 of this convenient form of fuel, which has never 

 come into public favour in this country, although 

 il is deservedly popular on the Continent. This 



