Feb. 25, 1886J 



NA TURE 



403 



seen, as compared with the dimming oft" of those parts of the solar 

 atmosphere which are farther removed. 



Now, can we watch this ? Can we study it so that we can 

 find out all about it? Well, not entirely. The photosphere 

 which carries the spots to which I have referred allows us 

 certainly to see the phenomena of the spots, but then it acts as a 

 veil that prevents us seeing anything nearer the centre of the 

 sun, whatever it is. It practically serves as a veil for all the 

 underlying phenomena. Also, as I have mentioned, the outer 

 corona is only visible for a few minutes in each generation ; so 

 that, when we attempt to watch the totality of the phenomena 

 from the top of that magnificent radius down to that part of it 

 which cuts the photosphere, there are difficulties of every kind 

 supervening ; we can only continuously and eftectively study 

 those regions of the atmosphere just above the photosphere, or 

 in other words the phenomena included in the inner corona. 



Absorption of the Suit's Atmosphere 



But in addition to this there is something else that we can do, 

 though this work is not so valuable, as its results are too general. 

 We can study the general absorptive efiect of the whole atmo- 

 sphere above the photosphere by dealing with ordinary sunlight 

 reflected from a cloud. 



The three kinds of absorption which we recognise in spectrum 

 analysis are these. First of all, we have a selective absorption 

 which enables us to determine the presence of the incandescent 

 vapour of any particular metal in the atmosphere of the sun. 



Ne.xt it was pointed out in the year 1873 ' that the absorption 

 of some elementary and compound gases is limited to the most 

 refrangible part of the spectrum when the gases are rare, and 

 creeps gradually into the visible violet part, and finally to the 

 red end of the spectrum as the pressure is gradually increased. 

 It looks very much as if all the permanent gases, or all gases 

 and vapours at a temperature below that which enables them to 

 give out bright lines or flutings, really possess this kind of ab- 

 sorption, and we know that the absorption of that kind at the 

 sun is enormous, because the blue spectrum of the electric light 

 is very much longer — si.x or seven or eight times — than the spec- 

 trum of the sun, because we get an ultra-violet radiation from the 

 electric light which has been stop|]ed in the atmosphere of the sun. 

 As there are permanent gases in the sun's atmosphere the 

 same conclusion is good for it also. If this absorption both here 

 and at the sun were taken away, it is clear that the sunlight would 

 be much bluer than it is at present. Prof. Langley, of the 

 United States, who seems to be unaware of the results arrived at 

 in 1873, has recently made the same announcement. 



There is one other kind of absorption also. We have a 

 general absorption — an absorption working equally up^n all 

 parts of the spectrum, which we may call general absorption in 

 its true sense — such absorption, for instance, as we should get 

 by mixing soot \yith water or smoking a glass and holding it in 

 front of the sun — this would cause a considerable dimming of 

 the light. 



We can make this general examination of the atmosphere of 

 tlie sun by simply observing the spectrum of sunlight reflected 

 from a cloud ; but it will be readily understood that, although 

 in that case we shall be able to study the indications of selective ab- 

 sorption and the absorption of the blue end of the spectrum due to 

 such gases as chlorine, and the general absorption of the spectrum 

 due to the existence of solid particles ; it will still be an inquiry 

 which will only deal with the matter in its most general aspect, 

 and we shall not be able to localise the exact regions in which 

 these absorptions take place. Further we may say that the 

 result of this study of the absorption of the solar atmosphere 

 taken as a whole is chemical and statical merely. There is 

 nothing dynamical about it. It tells us most important facts con- 

 cerning the chemical constitution of the sun's atmosphere, taken 

 as a whole, without localising the region in which any par- 

 ticular substance which we find to be absorbing is absorb- 

 ing ; but it does not tell us whether this atmosphere of the sun, 

 which roughly we may accept as about a million of miles high, 

 is in violent movement, or whether it is at rest. 



There is, then, very much more to be done before we are fully 

 in presence of the causes of the phenomena to which I have 

 called attention, which stare us in the face every time we look 

 at the sun, either when it is eclipsed, or when it is not. 



J. N. LocKYER 

 ( To he €011 tinned. ) 



SCIENTIFIC SERIALS 



The numbers of the Joiirna! of Botany for January and 

 February contain no papers of very great importance. Messrs. 

 H. and J. Groves record the addition of two new species to the 

 British Characese : Chara intermeJia and Nitella capitata, with 

 figures of both. — Mr. J. G. Baker attempts to trace the relation- 

 ship between the British and the Continental forms of the difficidt 

 genus Kubiis. — Another addition to the British flora is recorded 

 m Equisetum littorale, by Mr. W. H. Beeby. — Most of the other 

 articles relate to descriptive or geographical botany. 



The most important paper in the Nuovo Giornale Botanico 

 Italiano for January is an account by Sig. F. Morini of a new 

 disease of cereal crops caused by the attacks of a hitherto un- 

 described parasitic fungus, Sphisrella exitinlis, allied to 5'. 

 graminicola z.x\A S. Tassiana. — Sig. Pichi investigates the nature 

 of the reddish-brown spots on the stem of Bunias £ruea^o, 

 which he finds to come under the head of glandular emergences ; 

 and Sig. Cavara describes some singular anomalies and mon- 

 strosities in the flowers of Lonicera. 



SOCIETIES AND ACADEMIES 

 London 



Royal Society, January 14. — "The Coefficient of Viscosity 

 of Air." By Herbert Tomlinson, B. A. Communicated by 

 Prof. G. G. Stokes, P. R. S. 



The author etriployed the torsional vibrations of cylinders and 

 spheres, suspended vertically from a horizontal cylindrical bar, 

 and oscillating in a sufficiently unconfined space. The bar was 

 suspended by a rather fine wire of copper or silver attached to 

 its centre, which, after having been previously subjected to a 

 certain preliminary treatment with a view of reducing the in- 

 ternal molecular friction, was set in vibration. 



The coefficient of viscosity of air was obtained from obser- 

 vations of the diminution of the amplitude of vibration, pro- 

 duced by the resistance of the air to the oscillating spheres or 

 cylinders attached to the horizontal bar, arrangements having 

 been made so that the vibration-period of the wire should 

 remain the same, whether the cylinders or spheres were hanging 

 from the bar or not. In deducing the value of the coefficient 

 of viscosity from the logarithmic decrement, the author has 

 availed himself of the mathematical investigations of Prof. G. G. 

 Stokes. 1 



■ Five sets of experiments were made with hollow cylinders and 

 wooden spheres, in the construction and measurement of which 

 considerable care was taken. When the cylinders were used 

 arrangements were made to eliminate the eft'ect of the friction of 

 the air on their ends. The following are the results : — 



Phil. Tra 



vol. cl.v 



Cylinders 



V.bration- 

 period in 

 seconds 



deg 



Coefficient of 

 viscosity of 

 ■thef' 



Centigrade CG.S. units 



1202 ... O'0O0l8l7I 



I4"63 ... 00001S122 



If69 ... o'oooi8o24 



. I0'64 ... o'oooi7845 



60-875 ••■ 2-5636 ... 6-8373 



60-885 •■■ o'9636 ... 7'o59o 



60-875 ••■ 2-5636 ... 3-0198 



53-175 ... 2-5636 ... 2-9994 



Spheres 

 6-364 ... 2-88oi ... 9-35 ... 0-00017820 



Maxwell has proved - that the coefficient of viscosity of air is 

 independent of the pressure and directly proportional to the 

 absolute temperature. We can, therefore, calculate from the 

 above data what would be the value of the coefficient of vis- 

 cosity at o'' C. ; and when this is done, in the case of each of the 

 five sets of experiments, we obtain the following values : — 



Set of Coefficient of viscosity 



experiments ofairato°C. 



tst 000017404 



2nd ... ... 0-00017201 



3rd 0-00017284 



4th 0-00017359 



5th 0-00017230 



The mean of these numbers is 0-00017296 with a probable 



' See Prof. Stokes's paper "On the Effect of Ihe Internal Friction of 

 Fluids on the Motion of Pendulums," Trans. Camb. Phil. Soc, vol. ix. 

 Part II.. 1S50. 



= Phil. Trans., i366, vol. civt. Part I. 



