594 



NA TURE 



[April 23, 1903 



from A 434 to X 487. A spectrum of the Nova obtained 

 on February 17, 1903, does not agree with the spectrum 

 of the nebulosity at all. 



Prof. Perrine arrives at the conclusion, from the evidence 

 given by these spectrographs, that the results do not oppose 

 the theory that the light of the nebulosity — as considered in 

 that part of it called condensation D — is due to the reflec- 

 tion of the light emitted by the Nova at the time of its 

 greatest brightness, although, in face of the contradictory 

 evidence already published, he does not consider his con- 

 clusions strong enough to prove the reflection theory (Lick 

 Observatory Bulletin, No. 33). 



STELLAR PARALLAX. 1 



FOR three years, from 1893 to 1896, Mr. A. S. Flint, of 

 the Washburn Observatory, has devoted himself in- 

 defatigably to the determination of stellar parallax, and 

 his results, contained in the eleventh volume of that observ- 

 atory's publications, form a very handsome contribution to 

 this class of inquiry. Not only are these results of great 

 interest in themselves, but they offer a larger collection of 

 new material than has ever been made on a single occasion. 

 We have not onlv the observations of nearly a hundred stars, 

 but all arranged and discussed on one uniform plan, a not 

 unimportant factor in their bearing on the cosmical problem 

 to which such results are applicable. The stars are 

 scattered variously over the sky from the Pole to about 30° 

 S. declination, and have been selected to include stars of 

 considerable proper motion, a number of Prof. Burnham's 

 double stars which show proper motion, and some twelve 

 binary systems. 



The method of observation was that suggested and em- 

 ployed by Prof. Kapteyn, namely, the chronographic regis- 

 tration of the time at which the selected star and two 

 others, one preceding and one following, crossed the wires 

 of the meridian instrument. The total number of observ- 

 ations, fairly evenly distributed between the morning and 

 the evening, was 3659, all of which were made by Mr. 

 Flint, while he is also responsible for the heavy work en- 

 tailed in the discussion. Unfortunately, in this method of 

 observation it is necessary to employ screens, varying in 

 density, in front of the object glass, to reduce the light of 

 the more brilliant star to approximately that of the stars 

 of comparison. Experience has shown that very consider- 

 able errors are liable to be introduced in the determination 

 of difference of R.A. when this precaution is overlooked. 

 The ultimate value of the work will depend much on the 

 success with which the screens are applied, and this source 

 of error is eliminated. In this place we cannot enter fully 

 into the devices employed or the discussion applied to the 

 results. We can only say that the author has not found 

 it sufficient to trust to the mechanical devices alone, but 

 has had to submit his parallaxes to a further discussion, in 

 order to remove systematic errors, and we can very well 

 understand that this section of the work will be most care- 

 fully scrutinised by any astronomer who proposes to follow 

 in the footsteps of Prof. Kapteyn or Mr. Flint. 



The result of this examination is to determine a correc- 

 tion which the author has applied, and seeks to justify, 

 depending on the difference of magnitude and the right 

 ascension of the star. This correction can become so large 

 that it might make one hesitate to apply the method in 

 isolated instances, or wherever there is insufficient material 

 to permit an independent inquiry. The correction which 

 Mr. Flint applies to his parallax, or to the crude value re- 

 sulting from the solution of the ordinary equations of con- 

 dition, is |DM. y ; where ADM. is the difference between 

 the apparent magnitude of the parallax star and the mean 

 magnitude of the two stars of comparison, and y is given 

 by the expression 



y = +o"o67 + o"-ioi cos. R.A. 



If, then, the reduced light of the parallax star differed 

 by one magnitude from the mean of the other two, a correc- 

 tion of o"i68 might result, and inasmuch as a difference 

 of two magnitudes is not impossible, corrections of nearly 



1 Publications of the Washburn Observatory of the University of Wis- 

 < :onsin. Vol. xi. "Meridian Observations for Stellar Parallax." First 

 Series. By Albert S. Flint, Assistant Astronomer. Pp. 435 (Madison. 

 Wis. : State Printer, roo2.) 



four-tenths may be required, and in two instances o" 36 is 

 actually applied. This amount is a little startling, and 

 though it would seem ungracious to suggest more work 

 when so much has been attempted and carried to a suc- 

 cessful issue, one cannot but wish that the author had made 

 some complete sets of observations, without the use of a 

 screen at all. Then, in the case of such a star as 3 Cassio- 

 peia with its comparison stars, the amount of the correc- 

 tion would be some seven or eight-tenths of a second, a 

 quantity which could not have escaped detection. To those 

 who have not been engaged in similar inquiries it may 

 seem strange that the error in R.A. arising from the 

 observation of two stars of unequal magnitude is not 

 constant, and therefore disappearing in the parallax. It 

 may seem strange, too, that this puzzling discrepancy 

 should vary wilh the time of year, for that is what the 

 term depending on the right ascension practically means, 

 but it must be sufficient here to refer to the volume itself, 

 where the author has treated the matter in considerable 

 detail, and given his figures in the clearest manner. 



W. E. P. 



RIDGWAY'S AMERICAN BIRDS. 1 

 AT R. RIDGWAY is making good progress with his 

 laborious task, the first part of this work (already 

 noticed in these columns) having been issued in 1901. The 

 remaining volumes (probably six in number) are in a for- 

 ward state, and it is hoped may be published at the rate 

 of two a year. The present bulky volume is devoted to four 

 families of the Passeres, namely, the tanagers (Tanagrida;), 

 troupials (Icterida?), honey-creepers (Ccerebidae), and wood- 

 warblers (Mniotiltidae). 



The author's introductory remarks on the first of these 

 groups afford a curious comment on the prevalent prai tice 

 of dividing the Passeres into families. For the division 

 between the tanagers and the finches (Fringillidae) is stated 

 to be an arbitrary one, and the former group, as now re- 

 stricted, is confessedly more or less artificial. Indeed, it 

 is suggested that the fruit-eating forms (Euphoniae) may 

 eventually have to be separated as a distinct family group. 

 The author has already relegated to the Fringillidse 

 several of the genera included by Mr. Sclater among the 

 Tanagridae, while others he assigns to the Mniotillidae. 

 Moreover, the possession of only nine primary quills being 

 now regarded as an essential feature of the family, the 

 aberrant genus Calyptophilus must obviously find a place 

 elsewhere. Apart from the case of the last-mentioned 

 genus, all this suggests that, however convenient the 

 division into " families " of such an unwieldy group as 

 the Passeres may be for working purposes, such divisions 

 possess little title to be regarded as important morphological 

 units. 



In adopting the term " troupials " as the English equiva- 

 lent of the family Icteridae, the author is decidedly well 

 advised, and it may be hoped that the practice will be 

 adopted by future writers. In the definition of this family 

 the author makes the general absence or slight develop- 

 ment of the rictal bristles an important feature ; but no 

 reference to these structures is made in the main definitions 

 of the tanagers and honey-creepers, in which they may or 

 may not be developed. This, we think, is an omission, 

 although we are fully aware of the importance of making 

 definitions as concise as possible. The general plan of the 

 11 keys " appears, as in the first volume, excellent, and the 

 plates illustrative erf the beak, wing, tail, and foot-struc- 

 tures of the various groups described are equally satis- 

 factory. R. L. 



NO. 1747, VOL. 67 j 



,1 PERIODICAL OF PRECIOUS PLANTS. 

 T NDER the title of Flora and Sylva, a new monthly 

 ^ periodical has appeared, edited by Mr. Robinson, and 

 devoted to the illustration and description of " precious " 

 plants, fitted for cultivation in these islands. It is beauti- 

 fully printed in large type on good paper which allows of the 

 woodcuts being properly printed. The illustration of the 

 palmate bamboo on p. 3 is full of life, and forms a pleasing 

 1 "Birds of North and Middle America." By R. Ridgway. Part ii- 

 (Bii'l. U.S. Nat. Mus., No. 50.) Pp. xx + 834 ; 22 plates. (1902.) 



