April 28, 1892] 



NA TURE 



617 



of the dark lines relatively to the corresponding bright ones 

 gave a mean of i8'3 tenth-metres. According to this, the 

 relative motion of the two bodies engaged was about 820 miles 

 a second. Mr. Maunder also observed the visual spectrum of 

 the Nova. Three bright lines were seen, and estimated to be in 

 the positions of C, D, and F of the solar spectrum. A hne was 

 detected "not far from E," another "near b, but further towards 

 the blue," and another "very near the chief nebular line." 

 The line measured on the photograph as at A. 4919 was also 

 made out. 



Photographs of the Region of Nova Cygni.— At the 

 March meeting of the Royal Astronomical Society, Mr. Roberts 

 stated the results of a comparison of Drs. Copeland and Lohse's 

 catalogue and chart of the region of Nova Cygni with two 

 photographs of the same part of the heavens taken in Sep- 

 tember 1891. It appears that the brightness of some of the 

 stars has undergone changes since 1878, when the chart was 

 made. Changes of this character may, of course, be due to the 

 well known difference between visual and photographic magni- 

 tudes ; but there are other differences, which are not so easily 

 explained. Several stars, single on the chart, are seen to be 

 double on the photographs, and some changes in relative posi- 

 tion seem to have occurred. Although the Nova is not given on 

 the chart, it appears on the photographs as a star of about 

 magnitude 13. It will be interesting to compare Mr. Roberts's 

 pictures with others taken under similar conditions at some 

 future date, in order to determine definitely whether the changes 

 are real, or due to errors in observation or cataloguing. 



WiNNECKE' 



ing ephemeris 



s Comet. — Dr. 



in Astronomische 



R.A. 



G. F. Haerdtl gives the follow- 

 Nachrichteii, No. 3083 : — 



Decl. Brightness. 



2-38 



2-71 



3-IO 



3-58 



4-17 



4-91 



5-84 



7-04 



Personal Equations in Transit Observations. — An 

 accurate determination of an observer's personal equation is 

 to-day of as much importance as an observation itself, when such 

 small quantities, as we now deal with, have to be measured. 

 The variation in the latitude, of which we have heard so much 

 of late, amounts to a quantity only a few times larger than that 

 of a moderate personal equation, showing that no small regard 

 must be paid to its estimation. In observing an N.P. D., the star 

 has to be bisected by the horizontal wire, while the nadir point 

 has also to be observed : in both these cases an error can arise 

 from personality, for the best observers cannot make a really 

 true bisection. In the taking of transits another personality 

 exists, but this is rather of a different kind, for, using the eye 



NO. 1174. VOL. 45] 



and ear method, the clock beats have to be taken into account 

 simultaneously with the relative positions of the star and certain 

 wires. In the April number of the Bulletin Astronomique, 

 an account is given of some experimental researches on such 

 transit determinations in which both methods, the eye and ear 

 and the chronograph, were used. The observations were made 

 with an apparatus similar to that designed by Wolf, who, to 

 obtain artificial transits, employed a small truck to carry the 

 plates, on which punctures of different sizes were made. From 

 115 observations made with both methods, it was found that 

 equally accurate results were obtained, the eye and ear method, 

 if any, proving a little inferior, while the degree of lighting of 

 the field made no appreciable variation on the personal equa- 

 tion. For planets the electrical method showed that personality 

 varied considerably, according to whether the preceding or fol- 

 lowing side was observed : the resulting personal equation for 

 the centre of a planet turned out to be - 00463., while that for 

 a star under the same conditions was -f 0-0235. It would be 

 interesting to find out whether this occurs when the eye and ear 

 method is employed. The tendency of an observer, adopting 

 the eye and ear method, to choose certain tenths of a second in 

 preference to others, seems to have its analogy in the chrono- 

 graph method, in the linear measurement from the second im- 

 pressions. A comparison given here shows that the most 

 favourable tenth is the zero, while the nine is very considerably 

 left out in the cold. Another very curious fact is that the tenths, 

 one, two, three, four, chosen in the chronograph methods, 

 are all less than the corresponding ones in the other methods, 

 while the opposite occurs for the tenths five to nine. 



Tenths o i 

 Eye and Ear . . 157 97 

 Chronograph . , 164 79 



The Sirius System.— Dr. A. Auwers contributes to the 

 Astronomische Nachrichten, Nos. 3084 and 3085, a long dis- 

 cussion with reference to our " Knowledge of the Sirius System." 

 The problem which he undertook was to investigate whether 

 the measures of the companion obtained durmg the period 

 extending from 1862 to 1890 would satisfy an ellipse with a 

 49-4 year revolution ; to determine the most probable value of 

 the place elements for every measurement on the assumption of 

 the revolution ; and to inquire whether the observations of the 

 principal star could be represented by means of the so 

 determined elements. The author divides the discussion into 

 the following three parts : — (i) A summation and sifting of all 

 the measures that have been made of this companion for the 

 above mentioned period. (2) The derivation of the normal 

 places, and the correction of the elements. (3) A comparison 

 of the meridian observations of Sirius with the elements derived 

 from the measurements of the companion. The result of the 

 discussion is that a slight correction is necessary to reduce the 

 right ascension and declination of the bright star to the 

 centre of gravity of the two bodies (the masses of the chief star 

 and of the companion being taken as 2-20© and 1-040). 

 The table showing these cnrrections indicates that the right 

 ascension between the years 1850 and 1890 has to be in- 

 creased by a quantity which reaches to 0-232S., while between 

 1890 and 1896 5 a diminution takes place. The greatest 

 correction for the declination is + 2"'268, which occurs in 

 1882*0, and this correction becomes negative also about 1893-5. 



THE ANCIENT CIVILIZATION OF 

 CENTRAL AMERICA. 



N Central America there are abundant traces of the existence 

 of a great race which must at one time have att lined to a 



I 



comparatively high slate of culture. It was undoubtedly a race 

 of American Indians, and as undoubtedly closely connected 

 with the present Indian inhabitants of the country. 



No trace, however, of the ancient culture and knowledge 

 can be found amongst the Indians of to-day, and the numerous 

 ruins which lie scattered over the coiintry are the remains of 

 towns which have neither names nor history attached to them. 



Very little information can be gathered from the published 

 writings of the Spaniards who overran the country at the close of 

 the fifteenth and beginning of the sixteenth centuries ; but, apart 

 from their bearings on Spanish history and biography, these 

 writings have received very imperfect examination and criticism. 



The Spaniards have been severely censured for their remiss- 



