1 2 , [ g 1 8 



NATURE 



285 



northern hemisphere. Phi second, as well as the first, 

 represi nl stable conditions, 

 iliu^ .1 depression revolving with high speed in a 

 ion in the northern hemisphere is 

 imicall) possible. In practice evidently such a 

 a largi scale, as 

 the rotation th would inevitabh cause the 



turning movemenl to commence in the normal direc- 

 tion. On a small scale, however, eddies round 

 prei ipitous hi adlands might 

 evidenth be set up with revolution in either direi 

 I; appears from the above thai such rotation onci 

 .] ma; , undi r favourable' 1 onditions, pi 1 sis 

 P into a dust whirl or tornado, with revolution 

 cloi kwise or counter-cli to the 



initial impulse. One cannot impress 

 rongly on all observers of such phenomena the 

 iting in whii h direi tion the rotation 

 J. S. Dines. 

 . S.W. j, 1 )■ . ember ,s- 



Fuel Economisers. 



W'iiii regard to the fuel economiser designed b\ 



1 ■ I ti 1 -., and desci ibed in Nati be ol 



. I ma\ mention thai 1 have 



been making experiments in the same direction. 



In thi 1 1 rtomisei 1 on- 



ui-iil. i! metal box fixed over 



the upper pari of the grate. The products from the 

 led b\ a horizontal flue above the fire into 

 the lowei pari "I the box, in which they ascended 

 and heated it, after which the) were drawn back 

 tn the chimne\ b\ a flue ovei the one by which the) 

 entered, ["he result was a considerable increase in 

 the fire, but on removing the box 

 to make somi check readings under ordinary condi- 

 tions it was found that the arrangemi nl was imprac- 

 I h. flues were so coated with sool that it 

 was evident thai the l>ox would require to be too 

 frequently taken oui for cleaning to make it worth 

 I fear Prof. I<«.\^'~ arrangement will 

 be liable to the sain, disadvantagi . I should, how- 

 . mention that the coal used b) me was not 

 and was very smok) . 

 With regard to the objectionable appearance of these 

 omisers, 1 ma) state thai theii appearance can 

 be improved by painting them with suitable colours, 

 is nol necessar) r " use Mack. All paints- with 

 tin- exception of aluminium with which I am 

 acquainted radiate equally well for heat of wave- 

 is given mil al 1 It- temperatures employed. 

 White, or am colour, is as good as black for the 

 lh. same remarks apply to colours with 

 which hot-water radiators ma bi painted. Thi 

 ...lour which harmonises lust with their surroundings 

 may be used without reducing their efficiency. 



1 .a the hi al losi in thi ordinar) loosi I) 



might be saved if tin- fitting in was 



modified in th.- following wa) : ["hi bottom of the 



chimt 1 by a large sheet of metal, so 1 



make the fireplace-opening into a closed chamber; tine 



is drawn forward t\\.. or threi inches 1.. allow 



1 ulation of air into and out of this chambei 



at the hack of the grati , while the lire is pro- 



vided with a chimney passing through the sheet of 



metal forming the roof of the chamber. By ibis 



arrne. air heated b) the hoi bad; of the 



. which now goes up ilv chimney, would be senl 



into the room. In new grates i> might be advisabli 



to increase the amount of heat communicated to the 



ind als ' iack sui fa. e 



projections, lanj I treat as the 



heal m-fires, il is admitted by all that 



NO. 2563, VOL. I02] 



ii is our kitchen-ranges which an coal con- 

 sumers and where improvement is mosl urgentl) 

 1 'lied for. John Aitken. 

 Ardenlea, Falkirk, November 30. 



The trouble of cleaning referred to b) Dr. Aitken 

 has not in practice been found more than a minor 

 nconvenience, and provision to make 



ti .1 in the design. 1 agr : Dr. Vitken 



that, considering the radiating powei al there is 



nothing in the ...lour, but it is desirable nplo) an 



"enamel" stoved on so as not to smell ii the tem- 

 perature is raised, and I do not know that this can 

 be done equally well with colour. While saving of 

 fuel is most imp. .1 unit and urgent at the present time, 

 . quable distribution of heat about a rooirl has also its 

 advantages, and it remains to be seen if this resull 

 brought about b) my device will nol itsell more than 

 compensate hereafter for the presence of the un- 

 obtrusive, if somewhat plain, heat interchanges 01 

 "heavenly twins" as the) wen called b) the first to 

 bem lii b) theii pi esem e. C. V. Boys. 



A Mistaken Butterfly. 



I\ Nature of September 5 last an Australian corre- 

 spondent notes lb.' attraction of the blue knob of a 

 hatpin for a butterfly. When playing golf in Gulmarg 

 I Kashmir) this summer I was frequently put off by a 

 large butterfl) settling on the ball jusl as I was 

 making a stroke. 1 make a point of keeping m\ 

 ball white and clean, and the butterflies evidently 

 mistook ii for a white flower. S. Robson. 



Prince of Wales College, Jammu, 

 October 27. 



CHEMICAL CORRELATION IX THE 

 GROWTH OF PL l.VV.s. 



WHEN the apical shoot of a fir tree is broken 

 off or injured, it is a familiar fact that one 

 uf the lateral branches belovs changes its direction 

 of growth in order to take the place of the original 

 apical shout. The change of direction is accom- 

 panied by greater vigour of growth. These pheno- 

 mena attracted the attention of Ecrera, 1 who sug- 

 gested, as the reason why the lateral shoots do not 

 tend to grow vertically while the apical shoot is 

 intact, the possibility that the latter might produce 

 inhibitory substances of a chemical nature which 

 travel downwards to the other parts of the tree. 

 Direct evidence was not then available, but the 

 hypothesis has since received confirmation from 

 certain experiments by Dr. Jacques Loeb, who 

 appears to have been unaware of Errera's sug- 

 gestion. 



Although the phenomena are of general occur- 

 red .. Dr. Loch found the tropical plant, Rryo- 

 phyllum culvcinuin, an appropriate one for the pur- 

 pose of investigation. The stem carries a series of 

 ich in the axil of a leaf, while the leaves 

 themselves are also provided with buds in notches 

 around their edges. Under ordinary conditions all 

 these buds are dormant. Rut they can be made 

 10 grow by various procedures. The common ex- 

 periment of taking a willow shoot, cut ling off 

 the leaves and suspending ii horizontally in moist 



1 Brit. As^. Reports, 1904, p. 814. "Conflits de pittance e 

 nhibiioires chc/ les ve'giiaux,' Bull. soc. roy. I. tin. belgiquc, vol. xhi., 

 004 ; reprinted in "CEuvres Physiol. G Bruxelles 



