212 



KNOWLEDGE 



[November 2, 1891. 



THE UPPER ATMOSPHERE. 



By A. C. Eanyard. 



I AM enabled this month, through the kinduess of 

 Mr. Shadbolt, to lay before the readers of Know- 

 ledge some photographs taken from baUoons at 

 various altitudes. Mr. Shadbolt is a very experienced 

 amateur aeronaut who has made over sixty ascents, 

 and he was, I understand, the first to take a recognizable 

 photograph fi'om a balloon, in June, 1882. The rays of 

 light which fall on a photographic plate exposed from a 

 balloon have had to pass twice through the densest and 

 most dust-laden strata of the atmosiDhere. Even in photo- 

 graphing distant landscapes from the surface of the ground 

 very little detail is ordinarily obtained upon distant hills, 

 owing to the absorption of the photographically active rays 

 in passing through a great distance of the lower atmo- 

 sphere. But the difficulty is greatly increased in attempting 

 to photograph the distant earth from a great altitude in a 

 balloon, for not only is the absorption increased by the 

 long course of the rays through the lower an-, but the 

 observer sees the dust-motes in the atmosphere from their 

 sun-illuminated side. The veil of haze spread over the 

 earth, therefore, hides the objects behind it more effectually 

 than the transparent veil of haze which we ordinarily see 

 over a distant landscape, giving the soft effects of distance 

 which artists so well know. 



An observer with a giant telescope, on Mars or on the 

 Moon, would probably see much less of what is going on 

 on the surface of the earth than we are apt to imagine. 

 The white upper surfaces of the clouds would first attract 

 his attention, with, in between them, a very dim and hazy 

 view of objects on the earth's surface, rendered all the 

 more difficult to observe by the frequent presence of a 

 dazzlingly bright patch of sunlight reflected from the sea. 

 To a naked eye observer on Mars, the earth would 

 probably appear like a variable star, with a curious and 

 mysteriously irregular period of variation, due to the change 

 in the brightness of the specularly reflected patch of sun- 

 light as terrestrial clouds covered it up, or the rotation of 

 the earth brought continents or seas to the part of the earth's 

 surface from which specular reflection could take place. 

 The exposm-e of photographs taken fi-om a balloon 



published in the October number of KNOwLEDfiE. I have 

 only had an opportunity of examining the region under 

 unfavourable circumstances with an 18-inch reflector. It 

 seemed to me that the photograph showed many more 

 faint stars than I could reach with the telescope, and I 

 could only detect the brightest parts of the nebulous 

 regions. — A. C. Ranyard.] 



To the Editor of Knowledge. 



Sir, — There is some confusion in your September and 

 October numbers with reference to the magnitude of 

 Canopus : the magnitude O-l quoted in the list on p. 91 is 

 on the I'ranoiiu'triit An/fntina scale : the magnitudes of the 

 other stars, except « Centauri, are on the scale of the 

 Harvard Photometric (.'atalogue. and the two scales are 

 not comparable. Herschel's magnitudes are evidently not 

 photometric, and this introduces a new scale, and accounts 

 for the apparent faintness of Sirius. Thome gives the 

 magnitude of Canopus in 188.5 as — 0-6 with ZiiUner's 

 Photometer. The agreement is therefore complete as to 

 Canopus being the second brightest star in the heavens. 



In the October number, page 193, 2nd column, line 8, 

 " J Cancri " should road " S Caucri." 



Yours truly, T. W. Backhouse. 



must necessarily be short, for the balloon generally drifts 

 along with considerable velocity, and sometimes it revolves. 

 The revolution is, however, never very rapid, and it is 

 generally more noticeable as the balloon descends than as 

 it rises, owing to the greater irregularity of the car and 

 under-surface of the balloon as compared with the com- 

 paratively spherical surface which it presents to the air on 

 rising. With reference to the velocity with which balloons 

 travel, Mr. Shadbolt is of opinion that they do not, as a 

 general rule, travel so rapidly when at a considerable alti- 

 tude as they do when nearer to the earth. Since this is 

 contrary to the usually received opinion with regard to the 

 velocity of the wind at various altitudes, and ^Mr. Shad- 

 bolt's judgment is founded on very full notes which he 

 takes, during his balloon voyages, as to the time of passing 

 over various places, I give the following extract from a 

 letter he obligingly wrote me on the subject. Mr. Shad- 

 bolt says : " I have invariably found the wind near the 

 earth, say up to 1500 or 2000 feet, to be stronger than at 

 higher altitudes. I have frequently mounted up to take 

 refuge from an approaching squall, and it has overtaken 

 the balloon and passed below it, while nearly always when 

 above the clouds they appear to travel along at a more 

 rapid speed, and to pass along beneath the balloon. The 

 same thing is noticeable when there are no clouds ; you 

 take your bearings and scarcely seem to be moving imtil 

 you drop down near to the earth. Some might say that 

 this would naturally be due to the distance you are from 

 the objects below, making a quick movement appear to be 

 slow, but after some practice you learn to recognize the 

 actual rate at which you are passing over the gi'ound 

 below you." 



At considerably greater heights in the air than balloons 

 have ever attained to, the wind is known occasionally 

 to blow with a velocity of over 140 miles an hour. Thus 

 the dust from the explosion of Krakatoa, which took place 

 on 27th August, 1882, was carried to the West India 

 Islands (half round the earth) in seven days, and the 

 average velocity of the wind at mountain observatories 

 greatly exceeds the average velocity observed at the sea 

 level. A passenger in a balloon hardly feels the wind 

 from the time he starts till the time he touches 

 earth again, for though a high wind may be blowing 

 he is carried along with it, and only feels a slight 

 wind when the balloon, in rising or falling, passes 

 from one current into another, and then the sensation 

 only lasts until the balloon has taken up the velocity of 

 the current of air into which it has passed. The greatest 

 altitude which has been attained by a balloon seems to be 

 a little over seven miles. Mr. .lames Glaisher and 

 Mr. Coxwell ascended from Wolverhampton on the 5th 

 .September, 1862, and are believed to have reached an 

 altitude of 37,000 feet, at which height the barometer 

 would only stand at seven inches. Mr. Glaisher's last 

 reading in ascending was made at a height of 29,000 feet, 

 after that he became insensible, and Mr. Coxwell, at the 

 greatest height attained, lost the use of his hands, and was 

 obliged to pull the cord (which opened the valve and caused 

 them to descend) by seizing it with his teeth and bowing 

 his head downward. 



The altitude attained by Messrs. Glaisher and Coxwell, 

 though higher than the highest mountain, sinks into 

 insignificance compared with the total height of the ocean 

 of atmosphere which surrounds the earth. Small clouds 

 may occasionally be observed at a height of ten miles--' 



* Mr. II. 1'. C'ui'tis, of Boston, tells nie that the towering cuniulxis 

 clouds over thunderstorms on the Amei-ican pi-airies may sometimes 

 be seen on the horizon at a distance of 200 miles ; proving that they 

 oecasionallv attain an altitude of over five miles. 



