250 



NATURE 



[October 31, 19 12 



01 flint that we are asked to accept all sorts of in- 

 definite appeals to natural agencies as sufficient to 

 account for what no one, without uncommon faith in 

 the unknown possibilities of those agencies, would be 

 capable of imagining as due to any other agency than 

 the hand of man. 



To avoid, if possible, any misunderstanding, let me 

 say tliat the sub-Crag flint implements are not 

 ■•eoliths" in the sense given to that word by Mr. 

 Hcnjamin Harrison, nor in that given to it by M. 

 Rutot. Still less are they to be called "eoliths" bv 

 those who would apply that term to flints broken by 

 cartwheels or by the mill at Mantes. 



I propose to sketch in a later communication a pro- 

 gramme of inquiry into the nature and properties of 

 flint, the carrying out of which seems to me to be 

 urgently needed at this moment. 



October 29. E. Ray Lankestkr. 



High Tropical Winds. 



Last year, in a letter to the Editor of this journal (vol. 

 Ixxxvii, p. 415), I wrote about (he probable existence 

 of "upper trade-winds," according to the observation 

 of some high balloon flights at Balavia. Also I ven- 

 tured to explain the occurrence of high westerly winds 

 near the equator by supposing them' to be only feeble 

 winds of variable direction between the anti-trade 

 .md the upper trade. Finally, I mentioned my inten- 

 tion of continuing these researches by means of large 

 pilot-balloons. 



This has been done in the past vear, but the average 

 height reached by the balloons' was lower than" I 

 wished, owing to the inferior quality of some of them. 

 Notwithstanding this, the results' are of sufficient 

 interest to justify a short account of titem. 



Contrary to my expectations, I found the high 

 westerly winds (first met bv Berson on the Central 

 Africa expedition) not to be of secondary, but of 

 primary importance; moreover, not blowing under 

 but above the anti-trades. 



On four different occasions a balloon crossed the 

 upper limit of the westerly winds and again met 

 easterly currents. 



As I had already conjectured from the observations 

 made during the two preceding years (1910-11), the 

 anti-trade in the dry season (June-September) lies 

 higher than in the rainy season (December-March); 

 thus I found the average height of its upper limit to 

 be : — 



December-March 16-5 km. ( q cases). 



June-September 15-5 km. (18 cases). 



In the months of transition its direction may vary a 

 good deal, and then it is often difficult to disc'riminate 

 between the various current.s; notwithstanding, six 

 cases gave an average height of 15-8, i.e. a height 

 between those of the two monsoon seasons. 



Regarding the upper trade, I found it to be, just as 

 I expected, more obvious and at a higher level in 

 the rainy season than in the dry one, its lower limit 

 being : — 



December-March 17-0 km. ( g cases'). 



June-September 15-;, km. (13 cases). 



On the contrary, the high westerly winds were 

 found to occur in most cases during the dry season, 

 and at a height of more than ,17 km. 



Also in the months of transition their presence was 

 proved by some balloon flights; for instance, on April 

 24 and 27, iqi2, when two balloons burst at a height 

 of 27'2 and 2:;'3 km. respectively, and westerly winds 

 appeared to blow from 2o'o and i8'5 km. upwards. 



.\s _ already mentioned above, this year on four 

 occasions a balloon passed the upper limit of 

 the high westerly winds, viz. on January 24 at a 

 height of 23 km., and on September 7, 12,' and 23 at 

 about 24 km. 



NO. 2244, VOL. go] 



It is important to remark that Berson had already 

 seen this happen (at a height of 2o'2 km.) for the first 

 time at Dar-es-Salaam, but he must have under- 

 valued the height of the balloon, viewing it from one 

 point only, and making use of a theoretical rate of 

 ascent, in reality this rate increases strongly with 

 the height, as I have found by viewing my large pilot- 

 balloons from two points (2 or 4 km. apart). 



I estimate Berson 's pilot-balloon of 700 gr. must 

 have crossed the upper limit of the westerly winds at 

 about 23 km., accordingly at the same level as those 

 which ascended at Batavia. 



The balloon of September 12 burst at the enormous 

 height of 30,800 m., and gave evidence of the strong 

 easterly winds which have long been supposed to blow 

 at a great height above the tropical belt. 



Thus for the first time has been described the wind 

 which, during the period of 1883, August 27-Sep- 

 tember 8, carried the ashes of Krakatoa around the 

 earth at a level of ±30 km., and at a velocity of 

 34 m.p.sec, and therefore may properly be called 

 Krakatoa wind. 



The wind directions and velocities observed on 

 September 12 follow below : — ■ 



-Anlitiade wind 

 14 



19 

 13 



Upper liade wind 



"1 



II Mlinh west 



23 



eily winds 



8 

 5'\ 

 7 



9| 

 II 



19 



40 



33 

 34j 

 the same wind system 



Krakato.i wind 



reigned; as was proved by two balloons which reached 

 a height of 26'5 and 27^5 km. respectively. 



Regarding the explanation of the occurrence of 

 high westerly winds near the equator. Gold (Quarterly 

 Journal, 1910, p. 178) reminds us of the theoretical 

 results of Ovcrbeck, from which, according to him, 

 might easily be deducted that often at great heights 

 the vast westerly whirl around the poles extends over 

 the tropical belt. But the principles on which Over- 

 beck built his theory are not in agreement with" reality. 

 He regards difl^erence of temperature as the 

 ^rhna causa of the air-currents, and presumes the 

 vertical distribution of temperature to be caused by 

 conduction only, supposing other causes, such as 

 radiation, vertical currents, &c., to give an analogous 

 distribution as conduction gives it. 



