I ■ ARV 3O, 1919] 



NATURE 



425 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of. rejected manuscripts intended for 

 this or any other part of Nature. No notice if 

 taken of anonymous communications.] 



Cyclones. 



Mr. Deelbv's suggestion (Natukb, Jam:. 



p. 385 1 .luur is ( an- .1 bj (he high tem 



tun- m to be 



feasible for tin- following reason : Owing to the tem- 



ire inversion, or, a) least, to the cessation of the 

 rature with height, the boundary 

 betwi -sphere and stratosphere is,ingi n 



lefinite, as definite ahnosl as thi boundary 



n layers of ofl and wain- would be. If, then, 



oi sucking action — to use an incorrect but 



i,i. ni expression- were exerted by the lightness 

 of the air above (he boundary, it ought to draw up 

 the boundary itself as well as the air below it. This 

 is exactl) th ol what happens; the boundary 



bulges oul downwards in the cyclone and upwards 

 in the anticyclone. 



\ special case has just occurred. From January 4 

 to January 8 the barometer in England S.E. wa 



malry low, and observations on the upper air were 



11 d on January 6. The beginning of the strato- 

 was found at the low height of 75 km. — 

 io 7 km. i- 1 mperature of the strato- 



sphere was m r: ('. abovi for January, and 



the troposphere 6° below. Take thi analogous case 

 of a layer of >>il floating on a layer of water; 



disc of the "il be warmed by any means it will 

 expand outwards, and the same mass will rover a 

 larger surface, with the result that the common hori- 

 zontal boundary will rise. Conversely, if the oil be 

 cooled, the common boundary will sink. Exactly 

 the oppo-ite result was found on January 6. 



Rut if we postulate an outward radial sucking force 

 acting horizontally on the water just below the 

 common boundary, the water will rise from below at 

 the centre, the common boundary will fall, and the 

 laver of oil above will thicken, and this is just what 

 occurs in the layers of air. I have shown elsewhere 

 ijournal of the Scottish Meteorological Society, lot;, 

 p. 300) that on this supposition the observed changes 

 of temperature follow as a natural corollary, but I 

 do not see how an outward acceleration can be 



ed horizontally to the layers of air near the top 

 of the troposphere. W, H. Dims. 



I imiarv 17. 



Wiiii 1 ol cyclones is being discussed in 



\ vt 1 i;i .1 . ■ 1 niion in a point 



h I have ah 1 in a paper read bi 



I linburgh in January, 1016. It 

 is there pointed out that though the core of a cyclone 

 is colder than the core of an anticyclone or than the 

 nnding air, yet the air in the cyclone is lighter 

 than that in the anticyclone. This decrease in density 

 is due to the air being under a lower pressure. It is 

 shown that the lower pressure in cvclones more than 

 compensates for their lower temperature, so that 

 though the air in cyclones is colder, yet it is lighter 

 than the surrounding air, and tends to ascend in the 

 troposphere as well as in tin stratosphere. 



John Aitkf.n. 

 Ardenlea, Falkirk, January 17. 

 NO. 2570, VOL. I02] 



End-Products of Thorium. 



In a letter to N 1 0,17, Prof. Soddy 



thai 65 per cent, of thorium-l 1 upels first a 

 /3- and then an et-ray, ming into an isotope 



ni lead, and suggests that Ion the analogy of 

 radium-D) this isotope ol li ad may be further dis- 

 rated. Hi says that he h cted 1 In- presence 

 of thallium in thorite in amounts that sufficed for 

 chemical as well as for spectroscopic idi ntification, and 

 its that the lead isotopi [erred to may be 

 Formed into thallium owing to an a- and /3-rh 

 If thallium were an end-product of thorium, we 

 should expect that it would be found in all thorium 

 minerals, unless, of course, these havi been sufficiently 

 altered to account for the removal of the products. I 

 have lateK been engaged iti I lie examination of 

 thorianitc for Prof. Joly, the chief object of the in- 

 vi stigation being the determination of the proportion 

 of thallium, if any, and its relation to thorium. I 

 have not been able to detect any thallium in the 

 mineral, and I am confident that it does not contain 

 even 0005 per cent. J. R- Cotter. 

 Iveagh Geological Laboratory, 



Trinity College, Dublin, 'January 8. 



COMMERCIAL AVIATION AND THE 

 LARGE AEROPLANE. 



THERE is now no doubt that every possible 

 attempt will be made to utilise aviation for 

 commercial purposes, and that one of the first 

 questions to be settled is the choice of the best 

 type of machine for such uses. While small 

 machines of the "scout" type may be of con- 

 siderable utility for the rapid transport of single 

 passengers or small quantities of goods on special 

 occasions, it seems certain that the representative 

 type of the commercial aeroplane will be a large 

 machine capable of carrying considerable loads. 



Several very long flights have already been 

 made with large aeroplanes, and particular men- 

 tion mav be made of Gen. Salmond's pioneer 

 llight from Cairo to Delhi in December last, 

 when a distance of 3200 miles was covered in 

 45 hours' actual flying-time. In view of such feats 

 as this, it is obvious that the establishment of an 

 effective mail service is well within the capabili- 

 ties of existing aeroplanes, and merely awaits the 

 necessary capital and organisation. If, however, 

 the air is to be used as a medium for the trans- 

 port of goods in considerable quantities, machines 

 of much greater carrying rapacity than any yet 

 built will be required, and the question at once 

 arises as to the limiting size of machine which 

 can be satisfactorily designed. 



Much has been written on the subject of the 

 large aeroplane. An excellent survey of the 

 development of the present giant machines ap- 

 peared in La Nature for November 16 and 3° from 

 the pen of Lieut. Lefranc ; but the author did not 

 commit himself as to future possibilities in the 

 direction of increased size. Mr. Handley Page 

 has been very successful in building large aero- 

 planes, and his latest machine may be taken as 

 representative of the stage which has now been 

 reached. This machine has a span of about 127 ft., 

 and weighs 27,000 lb. when fully loaded. With 

 sufficient fuel for a 500-mile flight it could carry 



