287 4026 288

Cette courbe montre que RX Herculis appartient bien au type Algol.

J'ajouterai que sur les 847 observations que j'ai faites de cette etoile variable, 5 2 0 se rapportert A la periode de changement d'eclat et les 327 autres A 1'Cclat constant.

A m p l i t u d e d e l a v a r i a t i o n d ' ec l a t . La moyenne des 327 observatiom relatives B l'eclat

constant est de 8d32 de mon Cchelle cle lumitire; l'eclat minimum est de zd62, soit une amplitudc de ~ $ 7 0 .

D'autre part, en adoptant pour leri etoiles de com- paraison les grandeurs photomdtriques de l'observatoire de Potsdam, on trouve pour les eclats extrimes, 7 m 1 e t 7 m 7 environ ; avec les grandeurs de l'observatoire dHarvard Col- Ege, 6m9 et 7m6 environ; enfin M. Sawyer adopte 7410 et 7m5. La moyenne de ces diverses valeiirs est 7mo pour l'eclat maximum et 7m6 pour l'eclat minimum. Par suite, la valeur de I degre de mon Cchelle de lurni&re est voisine de om1 I

C o n c l u s i o n s . 1 0 . I1 resulte de nies observations que l'dtoile vari ' able RX Herculis aplpartient au type Algol. Ce resultat es

conforme A celui que donnent les observations de M. Sawye publiees dans The Astronomical Journal, No. 450 : La courb de lumihre obtenue avec ces observations, en les rapportar aux minima calcules avec les nouveaux elements donnes dan la presente note, montre en effet un eclat absolument cot stant peridant I 7 h environ.

2 0 . La durCe de periode est de zrhzorn3q55. 3O. La variation lumineuse est regulikre et sa d u d

est de 4h35m environ. Cette variation comprend une dim nution d'Cclat pendant zh 2om, et une augmentation pendar Zh IS".

40, L'eclat est constant pendant 1 6 ~ 45" environ. 5 0 . L'amplitude des variations d'eclat est de om6

Max. = 7910, Min. == 7 5 .

St. Genis-Laval, 1905 fevrier 'I I . M. Luizef.

Bmce Photographs of Planets. ( H a r v a r d C o l l e g e O b s e r v a t o r y C i r c u l a r Nlo. 97) .

In planning the Bruce 24-inch Telescope, it was ex- pected that it might be used for the discovery of faint satellites. Accordingly, photographs were taken of several of the planets, and an examination of those of Saturn re- sulted in the discovery of the ninth sat.llite, Phoebe. In photographic, as well as in visual work, it is much easier to confirm an object whose position is known than to make

of the plates, so far taken, which may prove useful in thi way. The name of the planet; the number of the plate i Series A ; the year, month and day; the Julian Day an decimal following Greenwich Mean Noon, corresponding t the centre of the exposure; the duration of the exposure and the right ascension and declination of the centre c the plate are given in the successive columns.

the original discovery. A list is according y given in Table I 1 -

T a b l e I. L i s t of P l a t e s .

4026

16 10

16 10

6 28 16 9

~

Object ~~~

Mars

Vesta W

>> ))

x n

,> Jupiter

B

>

-20.8 -20.8

+22.3 -22.3

Plate A

2192 2195

406 46 1

6108 6109 6116

__._-

6137

36

2 2

2 7

3550 3554 3556 3654 3655 3657 3658

3667 3669 3670

557 602

2650 2651 2654 3526 353' 3630 3632 3634 3635 3690

3666

7124 7126 7181

Date

1896 Dec. 28

1894 Mar. 23 x 2 7

1902 Aug. 2 0

1897 Jan. 5

x x 2 1

x )) 2 2

;) Sept. 2

1893 Nov. 18

i) 3 24 )> >> 2 5 >> )) 2 6 >, 1) 30

1894 Jan. 23 2 2 5

i, Febr. 2

1897 Aug. 14

x >) 30 x )) 3 I P June 26 )) >i 2 6 >) )) 2 7 D 3 2 7

. n 3 30 x 3 30 )> July I

)) )) 2 0

'899 May 29

x )) I

1894 April 26 n May 3

1897 Aug. 1 7 )) n 17 2 n 18

1899 May 16 )) - 2 2 0 w June 1 2 u I 3 >) )) I 4 D )) I 5 2) July 7

1905 Jan* 9 x x I 0 x D 24

The plates of Saturn are not given, since they are described in the Harvard Annals, Volume LIII. The faintest stars shown upon these plates may be estimated from the observations of Phoebe. This satellite appears on nearly all the good photographs in the region of Saturn taken with the Bruce Telescope, and having an exposure of more than an hour. It is barely visible with the Yerkes Telescope, which has an aperture of 40 inches, and attempts to see it with the Lick Telescope, aperture 36 inches, have so far failed. The computed limiting magnitudes corresponding to these apertures, are 16.8 and 1 7 . 0 . Allowing for the loss of light, due to the absorption in large lenses, the magni-

J. D.

3 92 2.5 39 3930.668 291 1.662 2 9 15.5 50 5982.506 5 983.5 1 7 5984.565 5995.633 2786.694 2788.655 2792.648 2 193- 5 7 7 2794.596 2 7 98,639 2852.556 2 854.5 63 2862.489 4151.492 4804.542 4805.5 7 7

4832.534 .589

4833.55 1 .625

4836.538 .595

4837.566 .623

2945.684 2952.646 4154.544

a593 4 155.5 5 1 4791.746 4795.862

48 06.5 Q 7

4818.694 4819.681 4820.67 7 482 1.7 74

6855.662 6856.648 6870.572

4843.589

- Exp.

3 5"

~

~

60 7 1 60 35 90

1 5 0

I 7 I 7 ' 5

'4 60 60 60 61 1 5

= 58 I 80 90

30 I74 30

124 30

30 60 5 7 60 60 6 0

164 '23 259 2 4 0

I 80 2 7 0

I 2 0

I 0

I 2 0

1 2 0

I 2 1

I 2 0

I 2 0

I 2 0

tA. 1900 ____ ___

4h 46" 4 38

11 7 I 9 7 I 9 8 I 9 23 I 9 1

3 36 3 34 3 33 3 3' 3 30 3 2 7

3 ' 7 3 '5 3 I4

1 1 9 I3 5 2

'3 53 ' 3 51 ' 3 54

I 1 I0

Iecl. 1900 ____

+25?1

-1-25.1

4-17.5 + '7.5 - 26.4 -26.7 - 2 5.6 - 30. I + 19.1 t 1 8 . 8 + 17.8 + 17.3 t I 7.8 t 1 7 . 8 + I7*3 + I 7.0 + I 7 . 0 + 6.5

- 10.3 - 9.9

+I0.2

- 10.2

tude of Phoebe may be assumed to be not far from 16.5. The faintest stars shown with the Bruce Telescope, with an exposure of one hour, may be assumed to be 17 .0 , and I 7.5 with an exposure of two hours, if the images are small and perfectly circular. If the images are elongated, much brighter stars may fail to be shown. While a very slight fogging permits somewhat fainter stars to be seen, the limit is soon reached and a moderate darkening of the plate cuts off all very faint stars. For this and other reasons an in- crease in the exposure does not produce a corresponding increase in the number of stars photographed. In some cases, an exposure of one hour shows as faint stars as an

exposure of five hours. We may therefore infer that should distant satellites brighter than the sixtechnth magnitude be discovered revolving around Mars, Vesti, Jupiter, Saturn, Uranus, or Neptune we may expect to find them upon the plates enumerated in Table I, and material may thus be de- rived for determining the periods with great accuracy.

As soon as the orbits of the sixth and seventh satel- lites of Jupiter are known approximately these photographs should serve to correct the elements, especially the period, if the satellites can be found on them. As their estimated magnitudes are 14 and 16 there should 3e no difficulty in finding them, as soon as their approximate places are known.

It was at first thought by Europeari astronomers that a mistake had been made and that the sixth satellite of Jupiter was an asteroid. It is curious that the writer when examining these very plates several years ago was tempted to make a similar mistake. An object was found on all the

plates taken in June and July, 1899, which moved slowly, like Jupiter, and did not leave a trail. It appeared to come to its stationary poiint at nearly the same time as Jupiter, and therefore seemed to be at about the same distance. It was actually an asteroid near aphelion whose slow motion was due to its eccentricity. The number of asteroid trails found upon these plates I S very large. No less than seven of them were marked upon Plate A 3550 by Dr. Stewart in 1899. It is difficult to identify them since they are not near opposition, which is the only part of their orbit for which the Berlin Jahrbuch n o w gives their positions. Approximate ephemerides, from the first to the second stationary points, are much needed. As stated, Annals LIII, 99, a very faint object was found by Mrs. Fleming which closely resembled a new satellite of Saturn, but which afterwards proved to be an asteroid.

Harvard College Observatory, 15105 April 2 0 . Edward C. Picker&.

tfber die Helligbeit I m Harvard Circular No. 95 (A. N. 4018) teilt Prof.

Wendell als das Resultat seiner photometrischen Messungen der Jupitersatelliten mit, dafl die Folge der Helligkeit immer 111 -I - I1 - IV gewesen ist. Auf den photographischen Platten der Kapsternwarte aus den Jahren 1891, 1903 und 1904 ist

Groningen, Mai 1905.

der Jupitersatellliten. die Folge unveranderlich I11 - I1 - I - IV. Das Interval1 I1 - I ist von derselben Groflenordnung als die Intervalle 111 - I1 und I - I V . Dies Verhalttiis ist sehr konstant auf allen Platten. Es mufl also die photographische Helligkeit mindestens eines Satelliten erheblich von der visuellen Helligkeit abweichen.

W. de Sitter.

uber den Veranderlichen R Coronae blorealis. Schreiben von Hofrat Prof. M. Wv in Konigstuhl-

Heidelberg vom 24. Mai. B Infolge der Aufforderung von Proft:ssor Pickering in

Astr. Nachr. 4017 habe ich R Coronae auf den besseren der vorhandenen Platten ausgemessen und findt: fur ihn folgende Helligkeiten :

Datum M. 2. Konigstuhl Hell. Instr.

Bei den grooeren Helligkeiten ist der Stern an die drei BD.-Sterne +27?2558, t-2802475 und t 2 8 0 2 4 6 9 an- geschlossen unter Annahme der Helligkeiten 4m0, 7423 und 7429 fur dieselben. Auf der letzten Aufnahme ist der Stern mit Plejadenaufnahmen durch Schatzung verglichen. R Co- ronae war am 7 . Mai eine Spur heller als der 3' nordostlich von ihm stehende Stern, den ich 11m4 schat2e.c

-

D

2

Schreiben von Prof. E. B e c k , Direktor der Sternwarte in Straflburg, vom 2 7 . Mai.

1893 Marz26 1 6 ~ 9m4 5m5 6Zoller 1894 April 2 12 45.0 9.1 18qq luni 17 11 43.0 5.6 . -

1 8 9 i Sept. 10 8.8 6.8 3

1899 Mai 19 10 51.9 6.4 )>

1903 )) 28 1 1 4.6 6.9 16Zoller 1905 )) 7 13 48.7 11.3 >>

sR Coronae bcrealis (s. A . N. 4017) wurde von ink gestern Mai 26 1 2 ~ IM. %. Straflburg i m 6 zoll. Refraktor im Anschlufi an die Sterne ?- und s Harv. Ann. 37 I ~ m o (nach Hagens Skala 9m85) geschatzt.<<

(58) Concordia. (345) Tercidins. Effemeride B. 1. 1907 Maggio 29, 30 concorda. Gr. 1 0 . 6 . A. Abetti. (470) Kilia. 1905 QM.

Kometen 1904 11, 1905 I1 und I905 a nicht mehr zu sehen Mai 31 und Juni I .

Korrektion der Ephemeride (A. N. 401 7 ) : Mai 29 + 19" --O!I. W. Luther.

Corr. all' effemeride (A. N. 4024): Giugno 3 -39" +or8 Gr. 1 2 . 2 - 12.3. E. MiZZosevich. Photographische Aufnahme von Got.: Juni 3 I a h 19m1 M. 2. K;onigstuhl a = I 5h 7m6 6 = - roo 7'

Gr. 12 .0 . M. Wov. y. Palisa.

I n h a l t zu Nr. 4026. C. M. Chestw. Observations 0' the Satellites of Saturn and Uranus in 1904. 277. -. M. Luizet. Sur l'ktoile variable RX Her- culis (Ch. 6636 a). 283. - .F. C. Picknizg-. Bruce Photographs of Planets 287. - W. de Sitter. uber die Helligkeit der Tupitersatelliten. 291. - Uber den Veranderlichen R Coronae borealis. 291. - Kleine Mitteilungen. 291.

Reschlossen 1905 Jnni 13. Herausg8:ber: H. K r e u t z . Druck von C. S c h a i d t . Expeditiou: Kiel, Nieinaunsweg 103.