462 



NATURE 



[August 3, 19 16 



to explain the contrasted experimental results of the 

 temperature effect of the large mass, and the lack of 

 it in the small mass. For, obviously, the tempera- 

 tures of the masses may now be intercnanged without 

 altering the value of the attraction if only the value 

 of B is constant. 



But, in the actual expyeriments by Dr. Shaw, might 

 not the heating of the large mass near the small one 

 possibly involve an increase of 5? And again, in the 

 heating of the small mass carried out by Poynting and 

 Phillips, the earth itself being the large mass, might 

 not the value of 6 be practically constant? If so, pos- 

 sibly the formula (la) here suggested might prove 

 consistent with all the experimental results just re- 

 viewed. E. H. Barton. 



Nottingham, July i8. 



The Gun-firing on the Western Front. 



In Nature for July 13 Dr. C. Davison directs 

 attention to Dr. van Everdingen's investigations with 

 regard to the propagation of sound, and he also refers 

 to the inaudibility of the reports in the face of a gentle 

 wind when the observer was comparatively near. In 

 this neighbourhood the sounds are heard distinctly 

 when a quiet situation is found, but a very marked 

 peculiarity is the fact that the direction of the wind 

 seems to make no appreciable difference in the in- 

 tensity of the sound. For example, on July 19 the 

 booming was very intense and quite easilv heard with 

 the wind blowing from the north-west. On the 20th, 

 with the wind from the east, the audibility was no 

 greater, possibly not so great. Westerly winds have 

 been frequent of late, but have not diminished the 

 sounds at all, whereas it is a fact that on some occa- 

 sions with an easterly wind no sounds were heard. 

 It is, of course, impossible to say whether there was 

 firing or not on these latter occasions, but it is cer- 

 tainly worth recording that on the majority of the 

 occasions upon which I have heard the sounds since 

 the end of 1914 I have at the same time observed 

 that the wind was westerly. 



Presumably in this neighbourhood we are beyond 

 the silent zone, and in the second-sound area, and 

 the suggestion seems to be that in this area the effect 

 of wind is negligible. Two further points worth 

 noting are the facts that the sounds here are practically 

 as intense as at Brighton, though we are about fifty 

 miles farther from the source, and also that the direc- 

 tion of the source is always fairlv obvious. 



The sounds being so distinct here, and having lost 

 so little intensity in the fifty miles which lie between 

 this neighbourhood and Brighton, it seems likely that 

 they should still be audible at much greater distances. 

 Possibly they could be traced to very extreme distances 

 with the aid of some very sensitive sound detector, if 

 any suitable instrument is available. 



it would also be interesting to get evidence from 

 aeronauts. Plenty of balloons are in use now, and 

 doubtless the sounds have been noted, if audible. 



C. Welborne Piper. 



Blackheath, S.E. 



Portraits of Wm. Smitit. 



In Phillips's " Memoirs of Wm. Smith," the father 

 of English geology, p. 125, reference is made to his 

 portrait, taken in 1805, by Solomon Williams, and 

 another by Jackson, and still another by Fourau, the 

 last presumably being now in the Geological Society's 

 rooms. So far I have been unable to trace the por- 

 traits by the two first-named artists. Can any of 

 your readers assist me? T. Sheppard. 



Museum, Hull. 



NO. 2440, VOL. 97] 



XATIONAL AFFORESTATION. 



SIR \V. SCHLICH, in an important article in 

 the Quarterly Journal of Forestry for July, 

 urges the importance of afforestation and dis- 

 cusses the measures which should be taken to 

 secure for the nation a sufficient supply of timber 

 in the future. The quantity of timber used in the 

 United Kingdom is enormous, and increases year 

 by year. In addition to the home production, esti- 

 mated at about 2,000,000 loads annually, there 

 was an import of 11,590,318 loads, valued at 

 33,788,884!., in 1913, as compared with 10,104,504 

 loads, worth 25,676,988/., in 1899. Only 10 per 

 cent, of the total timber imported in 1913 came 

 from British possessions, as against 22 per cent, 

 in 1899. All these figures relate solely to the raw- 

 material, timber; but there must be added wood 

 manufactures to the value of 3,583,187!., and 

 wood-pulp estimated at 4,617,739!,, entering our 

 ports in 19 13. We draw- our main supplies from 

 Russia, Sweden, Norway, France, the United 

 States, and Canada. In all these countries, except 

 Russia and Canada, the tendency in the future 

 will be towards restricted production, diminished 

 export, and increasing prices of timber, owing to 

 the annual growth in the forests not being suffi- 

 cient to replace what is taken away by cuttings 

 and by fores: fires. Our main imports are coni- 

 ferous timber, pitwood, and wood-pulp, three 

 classes of forest produce which can be profitably 

 produced in our climate. A review of the whole 

 situation shows that a considerable increase in the 

 area under timber in the United Kingdom w-ould 

 be economically sound, and would also ser\-e as 

 an insurance against an unexpected timber famine 

 brought about by international complications in 

 the future. 



Sir W. Schlich discusses at length the amount 

 and nature of the land available for afforestation. 

 As most forest work is done in winter, when agri- 

 cultural work is slack, a scheme of aflforestation 

 will provide extra labour for agriculture in spring 

 and summer, and consequently will be a consider- 

 able help to increased productivity of the land 

 generally. This point is of especial importance in 

 connection with small holdings, and should be 

 taken into account when considering schemes for 

 the settlement of discharged soldiers after the war. 

 Very large continuous forest tracts are not neces- 

 sary. Small blocks of woodland, with a minimum 

 area of 500 acres, scattered over the country in 

 the vicinity of small holdings, make an ideal com- 

 bination. Sir \V. Schlich summarises his pro- 

 posals for afforestation as follow-s : — 



(i) The afforestation of not less than 3,000,000 

 acres of surplus land, by planting about 30,000 acres 

 a year. 



(2) Private proprietors. Corporations, and the State 

 should take part in the work of afforestation, the State 

 doing that part which the other two agencies are not 

 willing or able to undertake. 



(3) Financial assistance should be given to private 

 proprietors in the work of afforestation, if necessary, 

 by making advances to them at the rate of interest at 

 which the State can take up money. 



To secure success from the verv outset it is essential 



