274 



NATURE 



ment and lateral movement, sometimes excessively intense, 

 giving indications of their being carried either to the right or 

 to the left of the picture by horizontal cm-rents. 



Such then is a first preliminary survey of the method of 

 observing the chemistry of the sun, not as a whole, but of eacli 

 particular little bit of the i-un, chosen here and there and 

 brought upon the slit of the spectroscope. ' 



J. Norman Lockyer 



SOME OBSERVATIONS ON THE MIGRATIO\ 



OF BIRDS' 

 YyHILE showing some friends the astronomical observat a-y 

 and accessories connected with the College of New Jersey 

 at Princeton, on the night of October 19, 18S0, after looking at 

 a number of objects through the gi-inch equatorial, we were 

 shovvn the moon, then a few days past its full phase. While 

 viewing this object my attention was at once arrested by numbers 

 of small birds more or less plainly seen passing across the field 

 of observation. They were in many cases very clearly defined 

 against the bright bacli ground ; the moven.ents of the wings were 

 plainly to be seen, as well as the entire action of flight. In the 

 same way the shape of the head and the tail were conspicuous, 

 when the bird was well focussed. As the moon had not been very 

 long above the horizon the direction of observation was conse- 

 quently toward the east, and the majority of the birds observed 

 were flying almost at right angles to the direction in which the 

 glass was pointed. 



Here then was opportunity for the determination of two points 

 —the kind of birds that were flying, and the general direction in 

 vrhich they were moving. Respecting the first, it was compara- 

 tively easy to decide as to what famdies the species belonged. 

 This point w as gained by observing the general shape of the 

 bu-ds, their relative size, the motion of their wings, and their 

 manner of flying ; that is, whether the flight was direct oruiidu- 

 latiiig, by continuous strokes of the wings or by an intermittent 

 motion of those members. 



Most of the birds seen were the smaller land birds, among 

 which were plainly recognised w arblers, finches, woodpeckers" 

 and blackbirds ; the relative numbers I eirg in the order of kinds 

 above named. Among the finches I would particularly mention 

 Chrysomitris tristis, which has a veiy characteristic flight ; and 

 the blackbu-ds were conspicuous by the peculiar shape of the 

 tail, from which characteristic I feel most positive in my iden- 

 tification of Quiscalus purpurcus. I mention such details to 

 explain just how observations were made and conclusions 

 arrived at. 



In regard to the second point, with rare exceptions the birds 

 were found to be flying from north-west to south-east. I do not 

 mean that this was absolutely the direction, but that it was the 

 approximate and general one. 



It is not within the scope of the present paper to do more than 

 give details on two other points, namely, the estimated number 

 of birds passing through a given space during a given time, 

 and the height at which the birds were most abundant. For 

 the basis of the first of these points it was necessary to note, 

 first, how many birds passed through the field of observation 

 per minute, and second, how near or how far distant from the 

 glass the birds would have to be in order to be seen at all, that 

 is to be in focus. 



The height of the moon above the horizon in degrees and the 

 two limits of the area of observation — that is how near or how 

 far the birds noted were from the glass— supply the data for 

 deteriiiining how high the birds seen were flying, and this, 

 combined with the number noted as passing per minute through 

 the field of observation, givts the basis for computing how- 

 many birds were passing through a square mile in a given time. 



In this connection it may be well to specify how the two limits 

 of observation were defined. The inferior limit, that is, the 

 nearest point where objects could be seen w-ith distinctness, was 

 easUy determined by the power of the glass ; this is about one 

 mile distant. The superior limit, or the most distant point, is 

 provisionally assumed to be not more than about four miles 

 away, on the hypothesis that the birds would not fly at a greater 

 height than ten thousand feet. It may appear, as future obser- 

 vations are inade, that this last limit is not correct, but the reasons 

 for assuining such a height as the superior limit are sufficient to 

 warrant its use in this case, for birds were observed on this same 

 night at a late hour when the height of the moon above the 

 ' From the Bulletin of the Nuttall Ornithological Club for April. 



\_7t(ly 21, 1881 



horizon would make the point at which the birds were noted 

 almost at this great elevation, viz. ten thousand feet 



I am greatly indebted to Prof. Charles A. Young for assistan,-e 

 in these observations, and with his aid have arrived It the con 

 filw°of f *^^^^■••->£^ number of birds passing though the 

 field of observation per minute was four and t half Prof 

 \oung has also kindly assisted me with the detatl s of the 

 problem in regard to the limits and area of the field • and he 

 foUowing diagram and computations are from his ttudy of the 



Moon's altitude = 30°; moon's semi-diameter = ic'o.;" The 

 aiea of observation is a flat triangle = B, A C From this Ji,,,, 



Area of triangle 15, A, C = 0-07020 miles. 



Area of triangle b. A, c = o 00439 miles. 



Therefore b, B, C, c = 0065S1 = ^i.^- mile. 



Distance from A to B = four miles. 



Number of birds seen per minute — 45. 



Number of birds per square mile per minute = 68. 



W. E. D. Scott 

 [Mr. Scott's novel and important observations definitely esta- 

 blish on a scientific basis several points in relation to the migra- 

 tion of birds that have heretofore rested almost wholly on 

 conjecture and probability. 



We have, first, the fact that the nearest birds seen through the 

 telescope must have been at least one mile above the earth, and 

 may have ranged in elevation from one mile to four miles. It 

 has been held that birds w hen migrating may fly at a sufficient 

 height to be able to distinguish such prominent features of the 

 landscape as coast lines, the principal watercourses, and moun- 

 tain chains over a wide area. Of this, thanks to Mr. Scott, we 

 now have proof. It therefore follows that during clear nights 

 birds are not without guidance during their long migratory 

 journeys, while the state of bewilderment they exhibit during 

 dark nights and thick weather becomes explainable on the 

 ground of their inability to discern their usual landmarks — points 

 that have been assumed as probable, but heretofore not actually 

 proven. 



These observations further indicate that many of our smaller 

 birds migrate not only at night but at a considerable elevation — 

 far beyond recognition by ordinary means of observation. A 

 promising field is here opened up, in which it is to I'C hoped 

 investigation will be further pushed, not only by Mr. Scott but 

 by others who may have opportunity therefor. — J. A. Allen.] 



ON THE EQUIVALENTS OF THE ELEMEN- 

 TARY BODIES CONSIDERED AS REPRE- 

 SENTING AN ARITHMETICAL PROGRES- 

 SION DEDUCIBLE FROM MENDELEEFF'S 

 TABLES 

 T^IIE relatively quick succession of new elementary bodies 

 which has marked the last decade of scientific progress and 

 which must be considered as the result of chemical research, 

 pioneered and guided by spectroscopic study, has brought very 

 prominently into notice Mendeleeff's most remarkable law of the 

 periodicity of the chemical elements. 



Originally published in Russian in 1871, his memoir has since 

 been translated and reprinted by the author in the Moiiikur 

 ScientiJiqHc (July, 1S79), and thence has been translated into 

 some of the English i urnals. 



