456 



SCIENCE, 



[Vol. V., No. 122. 



it has attracted much attention. It is manifestly 

 produced in the upper regions of the atmosphere; for 

 it is best seen from elevated mountains, where it is 

 continually visible in clear weather. It is often hid- 

 den at low stations by the plentiful reflected skylight 

 that comes from the coarser dust of the lower atmos- 

 phere, even though the sky seem tolerably clear. It 

 has been astonishingly distinct here in Cambridge 

 through the past winter, on the clear anti-cyclonic 

 days, with north-west winds, following the withdrawal 

 of the cyclonic cloud-disk; and it attains its greatest 

 visibility between clouds, because much of the lower 

 dusty air is then in shadow, and does not outshine 

 the delicate colors of the ring. On some recent cloud- 

 le'ss but slightly hazy days it has been entirely invisi- 

 ble. 



I have not observed the connection between the visi- 

 bility of the ring and the changes of temperature and 

 formation of clouds noted by Professor Stone, and 

 should be glad to learn more details as to date of 

 observations, and as to closeness of the connection 

 in point of time. A comparison of observations on 

 these questions made at Colorado Springs (where I 

 presume Professor Stone made his records) and on 

 the summit of Pike's Peak would be very instructive 

 in this respect. 



The most remarkable point in connection with the 

 ring is its persistence long after the cessation of the 

 brilliant twilights with which it began. How is- 

 the volcanic dust or the ice dust that causes it sup- 

 ported so long? It seems incredible that dust could 

 simply float for a year and a half in so thin a medium 

 as the atmosphere at a height of ten or more miles. 

 Electrical repulsion has been suggested as a support- 

 ing force, and it may be somewhat effective above 

 the level of storm-circulation; but, besides this, it 

 seems possible that the peculiar properties of water- 

 vapor may give some aid. Wollaston long ago spec- 

 ulated on the limitation of the atmosphere at an 

 altitude where its gases were frozen. The solid parti- 

 cles would there fall till evaporated, when the gases 

 thus formed would rise again till frozen once more 

 by the cold of expansion. Putter and others have 

 recently reconsidered this process. Whether the 

 theory is applicable or not to oxygen and nitrogen, it 

 certainly is of importance when water-vapor is con- 

 sidered : for, as is well known, the elasticity and con- 

 densibility of this constituent of the atmosphere are 

 mutually antagonistic. The vapor tends to diffuse 

 itself to altitudes where the cold caused by its expan- 

 sion would require the condensation of a part of it; 

 and, although such perfect diffusion is prevented in 

 the lower atmosphere by the friction that the vapor 

 suffers in passing through the air, it does not seem 

 unreasonable to believe it may obtain at great alti- 

 tudes where a normal distribution of vapor must be 

 more nearly attained, and especially so at times when 

 an extra supply of both vapor and dust is shot high 

 out of volcanic craters. We may therefore believe 

 that at some high level the atmosphere is ' saturated ' 

 with vapor: above this there will be continual con- 

 densation, supplying a delicate shower of the minutest 

 ice particles; and, if these really need a solid nucleus 

 to freeze upon, the nuclei may be sustained by the 

 continuous upward diffusion of the vapor that rises 

 to take the place of that which has been condensed, 

 only to be condensed itself in its turn. Kiessling's 

 discussion of the diffractive action of particles sus- 

 pended at considerable altitudes fully accounts for 

 the twilights and the solar ring; and the close agree- 

 ment in date of occurrence of several great volcanic 

 explosions, and subsequent brilliant twilight displays, 

 naturally leads to the acceptance of the volcano as 



the source of the diffracting matter. Perhaps the 

 Wollastonian idea may aid in explaining the remain- 

 ing difficulty; namely, the long-continued suspension 

 of some of the diffracting matter in the upper atmos- 

 phere. W. M. Davis. 



Cambridge, May 24. 



Life. 



In the brief abstract in Science (May 8, p. 386) of 

 my address on ' Life,' at the celebration of the semi- 

 centennial anniversary of the Lyceum of natural his- 

 tory of Williams college, I am credited with the 

 following statement: "Kick a stone and a dog: the 

 difference in the result is caused by education." 



The words are printed in quotation-marks, as if 

 they were my own; and, as a friend tells me that they 

 seem to him to imply a belief that life has been pro- 

 duced by the education of dead matter, and that a 

 stone might be educated into a dog, I hope you will 

 give me space to say that the words are not mine. 



Beyond the quotation, with approval, of Huxley's 

 statement, — that "for us, at least, the distinction 

 between living bodies, and those which do not live, is 

 an ultimate fact," — the address contained no opinions 

 regarding the origin or cause of life. It was devoted 

 to the presentation of a definition; and I tried to 

 show, first, that education makes us acquainted with 

 the order of nature, and thus enables us to use one 

 event as the sign of another which is to follow, 

 and to regulate our actions according to the laws of 

 nature; and secondly, that, since all living things 

 respond to the order of nature in the same way, they 

 also are educated; and that education, or the ability 

 to make such responses, is life. 



The writer of the abstract in Science had no op- 

 portunity to consult my manuscript, but I believe 

 that the sentence which I have quoted is from his 

 notes on a passage which reads as follows: "The 

 actions of the dog are significant. They stand in 

 relation to the external world, and their meaning 

 could never be learned from the study of the dog's 

 body, but must be sought in his environment, and 

 that of his ancestors. The real difference between 

 living and dead matter lies in this significance of the 

 actions of living things. This is what we really 

 mean when we say that the dog is alive, while the 

 stone is not." W. K. Brooks. 



EBENEZER EMMONS. 



Professor Ebenezer Emmons was born at 

 Middlefield, Mass., May 16, 1800, 1 and died 

 at his plantation, Brunswick county, N.C., on 

 the 1st of October, 1863. 



He was prepared for college at Plainfield, 

 Mass., under the Rev. Mr. Halleck, entered 

 Williams college at the age pf sixteen, and 

 was graduated in the class of 1820. 



As a surgeon, Dr. Emmons ranked high in 

 his profession, and for fifteen years was the 

 most eminent practitioner in Berkshire count}'. 

 He was appointed professor of chemistry at 



1 His birth has been variously stated as in 1798 and 1799 ; but 

 he always stated to his children that he was born in 1800. 



