334 



NATURE 



\Feb. 7, 1884 



sensitive to a sudden change of pressure than even the most 

 delicate aneroid. 



It is strange that so few people have noticed this sensation in 

 the ears; besides Mr. Unr.-ice Darwin I do not know of any one 

 wlio I may say has been disturbed by it, 



During the gale on the 22nd and 23rd inst. it occurred to me 

 to try w hether I could get an idea of the pressure that could be 

 felt by the ear. My rorim faces west, and the wind was beating 

 against the windows ; so after shutting the door I opened one of 

 the windows suddenly during a furious gust, at which a small 

 gas-flame bobbed nearly out, and the same instantaneous sensa- 

 tion was plainly felt. On shutting it again the gas-flame started 

 up, but the inverse sensation was not perceptible. The gas-flame 

 stood at apparently the same height with the window shut or 

 open. Its movements were simply due to the starting and stop- 

 ping of an extra draught in the chimney. On examining the 

 meniscus at the top of the column in a mercurial barometer, the 

 change of pressure was plainly visilile, not hy a rise and fall of 

 the whole column, but by a change of curvature which was very 

 marked w hen the window was opened during the stronger gusts. 

 A pocket aneroid showed the same thing perfectly, rising, as 

 far as I could judge, about 1/150 inch in general, but during one 

 very furious blast 1/20 inch ; on that occasion only did the 

 shock on the ears seem at all comparable with what I remember 

 to have felt in the tunnels. 



It is not necessary to wait for a gale in the right direction to 

 test the ears. I found that if a friend charged the door with 

 his whole strength, much the same compression was produced as 

 by the average gusts of wind. Of course the compression w ill 

 depend partly on tlie contents of the room, which were, in the 

 case in question, about 2500 cubic feet. 



It is probable that the change of pressure noticed by the ear 

 is greater than that shown by the barometer, for the in tantaneous 

 effect on the gas flame was enormous, while the permanent action 

 was barely perceptible ; on the other hand, the aneroid showed a 

 permanent displacement with only a very slight recoil. The 

 greater mobility of the gas doubtless corresponds to the great 

 sensibility of the ear. 



If the actual change of pressure felt by the ear is 1/150 inch, 

 which corresponds to a charge of level of six feet, it might be 

 expected that a sensation would be ob-erved on running up or 

 down stairs. This I have not noticed, the change of pres.sure 

 being so gradual. 



I need hardly add that descending a mine at the high speeds 

 common in the collieries is most pamful to me, and is only ren- 

 dered bearable by continuously swallowing. 



The very great and apparently unrecognised difference that 

 there seems to be in the sensibility of the ears of different indi- 

 viduals may be an excuse for occupying so much of your valuable 

 space with what is in other respects a long and uninteresting 

 letter. C. V. Boys 



Physical Laboratory, South Kensington 



The Remarkable Sunsets 



In Nature for December 20, 1883, Dr. James Macaulay has 

 collected {pp. 176, 177) some recorded instances of the wide 

 distribution at former periods of volcanic du.st. Perhaps the 

 following may be worth adding. It is to be found in that extra- 

 ordinary repertory of curious information and suggestion, the 

 " Philosophical Notes" to Darwin's "Botanic Garden" (part ii. 

 3rd edition, 1791, p. 167). W. T. T. D. 



The Rev. Mr. Sterling gives an account of a darkness for six 

 or eight hours at Detroit in America, on October 19, 1762, in 

 which the sun appeared as red as blood, and thrice its usual 

 size : some rain falling covered white paper with dark drops 

 like sulphur or dirt, which burnt like wet gunpowder, and the 

 air had a very sulphureous smell. He supposes this to have 

 been emitted from some distant earthquake or volcano {PInl. 

 Trans, v. liii. p. 63). 



In many circumstances this wind [the Ilaimattan] seems 

 much to resemble the dry fog which covered most parts of Europe 

 in the summer of 1780, which has been supijosed to have had a 

 volcanic origin, as it succeeded the violent eruption of Mount 

 Hecia and its neighbourhood. From the subsidence of a white 

 powder, it seems probable that the Haimatlan has a similar 

 origin, from the unexplored mountains of Africa. Nor is it 

 improbable that the epidemic coughs which occasionally traverse 

 immense tracts of country may be the products of volcanic 

 eru:tions: nor impossible that at some future time contagious 



miasmata may be thus emitted from subterranean fissures in such 

 abundance as to contaminate the whole atmiphere and depopu- 

 late the earth (Darwin's "Botanic Garden," part ii. 3rd edition, 

 1791, p. 167). 



We had the sunset display again to-night, but the after-glow 

 was much less proIon<Jed, .suggesting that the stratum of dust and 

 crystals is slowly settling down. But repeated flashes of light- 

 ning and peals of thunder, in a place where storms, at the usual 

 time of year for them, are very mfrequent, seem to suggest also 

 the question whether the ash is not brought within the sphere of 

 rain-clouds rather by loss of electricity than the influence of 

 surface-gales. At the same time the large fluctuations of pres- 

 sure .seem to tell, on the contrary, that the whole column is 

 affected to unusual altitudes. .Since I have been a reader of 

 journals I have seen nothing more enthralling in its interest than 

 the contributions made, week by week, to Nature on this 

 subject from all parts of the world. It marks an era in obser- 

 vation from which we may hope great things in the future. 



Bregner, Bournemouth, February 2 Henry Cecil 



Referring to the latter part of Mr. Hawell's letter in 

 Nature, January 24 (p. 285), there seem to be several different 

 ways in which volcanic dust might affect the temperature, and 

 though all of them seem likely to have but small effect, the 

 quantities they affect are .'0 vast that a very small percentage 

 may form a very considerable quantity. 



1. The volcanic gases would form at first a stratum much 

 warmer than would be natural to the heights at which they 

 would rest, and would thus retard the outward flow of heat from 

 the earth. 



2. The volcanic dust, forming an unusually high stratum of 

 opaque matter, w ould. intercept rays from the sun that would 

 be otherwise lost to the earth. 



3. The volcanic dust would act as a screen to prevent the 

 earth losing heat by radiation, while it would also (4) act as a 

 screen to prevent tlie : un's rays reaching the earth ; but in so 

 doing would make the dust stratum warmer, ard so would aid 

 cau-e No. i. 



The indirect effects, as influencing evaporation and condensa- 

 tion, and the formation of clouds, are probably greater than the 

 direct, but ai'e more difficult to analyse. 



December 3. — I have noticed that December 3 was generally 

 remarl.ably cloudy. Here, however, it was conspicuous as the 

 day on which all the most marked features of the sunsets cul- 

 nniiated. At 4. 45 the green and pink glows covered the western 

 half of the sky, and the test of the sky was filled with a purple 

 glow of liKe character, while the crescent moon w-as green. 

 These glows had to a great extent faded at 5 ; and though the 

 phenomenon lasted late, I can give no more detail*, as I took 

 no notes, not being able to give it continuous attention. 



37, The Square, Ripon, January 28 W. \V. Taylor 



Christian Conrad Sprengel 



Steaking of Christian Conr.id Sprengel's discoveries, Dr. 

 H. A. Hagen says (Nature, vol. xxix. p. 29) : — "In Germany 

 these discoveries were well known to every naturalist during the 

 whole century. Certainly between 1830 and 1870 at every 

 university in Prussia the same facts were taught as well-known 

 facts of the highest importance, and of course known by every 

 student." From the complete want of papers relating to the 

 facts observed, and the theories proposed by Sprengel in the 

 German botanical and entomological periodicals published before 

 the time of Darwin, strangely contrasting with the profusion of 

 such papers in modern botanical literature, one might have been 

 led to a very different conclusi m, viz. that Sprengel had fallen 

 into almost complete oblivion in Germany also, and that hardly 

 any professor in any of the universities of Prussia and of 

 Germany in general duly appreciated and taught his discoveries 

 before Darwin's time. And this, I think, is really the case. 

 Certainly at the University of Berlin in 1841, neither Lichten- 

 stein, in his lectures on zoology, nor Kunth in those on botany, 

 ever spoke of Sprengel and his work, nor did Erichson in his 

 course on entomology. At the University of Greifswald, in 

 1842, the professor of natural history, Hornschuch, never men- 

 tioned Sprengel's discoveries. In 1848 my brother, Hermann 

 Miiller, began the .study of zoology aid botany at the University 

 of Halle, where he never heard of Sprengel, with whose work 



