March 9, 1876] 



NATURE 



367 



fluid and clear, the cobalt borate ball partly dissipated, and, on 

 cooling, the surface of the bead presenting a pink appearance, 

 evidently caused by projected particles of soda, volatilised 

 per se. 



6. It would thus seem that the blowpipe is even a more delicate 

 analytical weapon than the spectroscope, for it distinguishes 

 between two flames exhibiting D-line spectra only, which spec- 

 trum analysis does not. W. A. Ross 



March 6 



The Screw-Propeller in Nature 



Now that the question of the best form of the screw as a pro- 

 peller has become of such importance it is interesting to note 

 what Nature has done in this direction. 



The seed of the ash [Fraxinus excelsior) is provided with a 

 wing very delicately twisted, and, when the seed falls, the action 

 of the air upon this screw-like wing causes it to revolve rapidly. 

 The result is that the seed is kept suspended in the air for a 

 comparatively long time, and is wafted by the slightest breeze to 

 a considerable distance from the parent tree. I do not know 

 that this peculiarity is referred to in any botanical work, but it 

 very beautifully fulfils the object which characterises more com- 

 pletely the lighter- winged seeds, viz., the dispersion of the seed 

 beyond the limits of the plant or tree which bears it. 



I am not by any means sure that the screw on the ash seed 

 will not by its own action, independently of any wind, work itself 

 away, in its fall, from the perpendicular line. But, when the 

 wind blows strongly — and it takes a strong wind to blow the 

 seeds off at all — their range is very extensive. 



The seeds hang stubbornly to the tree through the winter 

 months, reserving themselves for the March gales, of which the 

 wind-fertilising plants avail themselves so largely. 



I should mucti like to know if any of your readers have ob- 

 served this screw and studied its pitch, and it would be very 

 remarkable should it prove that the pitch of this natural screw is 

 the one which will give the most power to the propeller of a 

 steamer. 



The seeds of the maple and the sycamore have somewhat 

 similar appendages, but the screw is, in neither case, so marked. 

 If anyone, at this season, will throw up a stick at the seed 

 clusters of ash, maple, or sycamore, he will find the seeds come 

 fluttering to the ground like a cloud of butterflies and alighting 

 quite as softly on the ground. 



Feb. IS Alfred George Renshaw 



The Migration of Species 



In Nature, vol. xii. p. 86, I read a communication signed 

 " W. L. Distant," in which the writer states that sea-going ships 

 were frequently visited by both birds and insects. 



In confirmation of this fact, I can mention from my own 

 observation two instances of birds visiting ships in which I was 

 making the homeward voyage from the West Indies, and one 

 instance on a voyage to New Zealand, in which the visitor was a 

 butterfly. 



In the first case, the ship being off the Spanish coast, but not 

 in sight of land, a veiy handsome bird came on board. It was 

 a species of dove, blue being the principal colour, with darker 

 markings. Some of the .seamen called it a Spanish dove. It 

 was caged and taken home by one of the passengers. 



In the second case, being in the neighbourhood of Bermuda, a 

 large flight of a species of swallow settled on the vessel. These 

 poor birds were in a very exhausted condition, and numbers of 

 them were captured by a large cat belonging to the ship. The 

 survivors continued their passage at daybreak next morning. 



In the year i86 — , on a voyage to New Zealand, we were one 

 morning visited by a butterfly, there being at the time a light 

 breeze blowing. My sons made great efforts to capture this inte- 

 resting stranger, but unfortunately without success, as it fluttered 

 overboard, and was soon lost to sight in the hollows of the 

 waves. They, however, got sufficiently near to ascertain it 

 to be a true butterfly. The colour consisted of various shades of 

 rich orange brown, and the margins of the wings were deeply 

 indented. 



1 made careful inquiries of the ofScers of the ship as to the 

 proximity of land, and was informed that the nearest was the 

 rock of St. Pauls, then fully two hundred miles distant. 



M. DASENT 



Patea, Taranaki, New Zealand, Nov. i8, 1875 



The Three Kingdoms of Nature 



Some children were playing at a game called " The King- 

 doms, " which consists in the mention of various substances, and 

 asking if they belong to the animal, vegetable, or mineral 

 kingdoms. One little girl mentioned " water," and the com- 

 pany were puzzled as to which kingdom it should be assigned. 

 Is there a sub-aerial or gaseous kingdom ? Will you kindly 

 enlighten the members of our Nursery ? 



March 4 



OUR ASTRONOMICAL COLUMN 



The Variable Star, ^ Persei (ALcaL). — Herr 

 Julius Schmidt, Director of the Observatory at Athens, 

 publishes in the Astronomische Nachrichten the results of 

 observations on the times of minima of this variable star, 

 extending from August 1846 to November 1875. The 

 epochs are given in Paris mean time with correction for 

 the light-equation. The probable error of a single deter- 

 mination of the time of minimum from 183 observations 

 by Schmidt is ± 80 minutes ; fifty observations of Arge- 

 lander gave a probable error of ± 6'o minutes, and fifty- 

 five observations of Schonfeld, one of ± 46 minutes, 

 showing by a mean of the 288 observations a probable 

 error of ± 70 minutes. The period assumed by Schmidt 

 in the discussion of his Algol observations between 1840- 

 1875 is 2d. 2oh. 48m. 53'6s. 



Some interesting details respecting this star are found 

 in Schonfeld's " Der lichtwandel des Stems Algol im 

 Perseus " (Mannheim, 1870). His comparison stars and 

 their relative assumed brightnesses were : — 



Star. 

 V Persei 

 a Trianguli 

 5 Persei 

 /3 Tiianguli 

 7 Persei 

 e Persei 

 )3 Aiietis 

 i Aurigse 

 7 AndromedcC. 



Brightness. 



o '9 in grades. 



35 



7-8 =, 



91 

 10-9 

 12-8 

 167 

 I7*3 



23-4 y, 



The following, extracted from the more extensive table 

 given by Schonfeld in his treatise, will indicate the law of 

 variation as derived from the light curve : — 



The most probable period over which the variation 

 extends is 9j hours, and the minimum lies very nearly in 

 the middle of the same. The most perceptible diminu- 

 tion of brightness occurs ih. 26m. before the minimum, 

 when the star is somewhat fainter than the mean of y and 

 e Persei, and the most perceptible augmentation when the 

 star arrives at nearly the same degree of brightness, but 

 ih. 47m. after minimum. In this phase it is hardly fainter 

 than the mean of h Persei and a Trianguli. Schonfeld 

 states that to his eye the variation of Algol is included 

 between the magnitudes 2'2 and 37 ; he considers y 

 Andromedae an average star of the second magnitude, 

 8 Persei 3"5, a Trianguli about 3'i, and v Persei 4"i. 



For elements of Algol we may adopt at present the 

 following, derived from Schonfeld's last catalogue. First 

 minimum of 1876 . . January 2*23233 Greenwich mean 

 time J period 2-867288. 



