Nr. 306.

sole de Gancbey dont ju~qu’ici on s’est uniformCment servi dans nos anciennes Etations d’Europe et tl’Asie. E n discu- tant cette question on dvaluera sans doute les avantages qui naissent, dans I’appareil de Mr. GauJs de la moindre mobi- lit6 des barreaux par des courans d’air, comme de la lecture &Ce et rapide des divisions angulaires en de trks petits intervalles de terns. Mon d$sir n’est que de voir &tendre les lignes de slations magndiques, quelques soyent les moyens par lesquels on parvienne B obtenir la pr6cision des observations correspondantes. Je dois rappclcr aussi que deux voyageurs inslruits, Mrs. Sartorius el Lis~ing, xnunis d’in- strumens de petites dimensions et trks-portatifs out employe

avec beaucoup de succes la mdthode dn grand Gdometre de Gcttingue dans leurs excursions ii Naples et en SiciIe.

Je supplie Votre Altesse Royale d’excuser l’dtendue des ddveloppemens que renferment ces lignes. J’ai pens4 pu’il seroit nlile de rdunir sous u n d m e point de vue ce qui B C t B fait ou prepare dans les divers pays pour atteiiidre le but d’un grand travail simultand sur les lois du MagnCtisme terrest re.

AgrCez, Monseigneur, l’bommage d u plus profond respect, avec lequel j’ai Phonneur d’dtre

De V. A. Ii. Berlin, en Avril 1836. etc. etc.

AZexandre de WumboZdt.

S c h r e i b e u des H e r r n H u s s e y au deli H e r a u s g e b e r . Rectory. Hayes Kent. January 1.

O n e of ttie most singular circumstances connected wit11 ttie recent reappearance of Halley’s Comet is, that , nolwith- standing the very different magnitudes of tlie instrunicnts em- ployed in the search, it was found by them all so nearly at the same time, that it may be designated without impropriely a contemporaneous discovery. O n Aug. 20 it was first secn By M. Strzwe at Dorpat. Ey him also on the 21, as well as by ill. Kunowsky at Berlin; Boguslawski at Ereslau; KoZler and Stampfer at Kremsmiinster j , and Littrow at Viennae, on the 22nd by myself and Sir Jamrs South.

Regarding therefore as contemporaneous the discovery by various astronomers of this interesting body, 1 would sug- gest an explanation of this curious circumstance grounded upon t h e following considerations.

That a refracting telescope shonld perform well, an exact correction is necessary b o t h of the spherical and chromatic aberrations. The former which may be subjected t o direct experiment *) is on illis account ninre manageable tlian the latter, which must depend upon tlie accwacy of the eye of the optician in judging the effect of his skill in applying un- erring principles. iYow i t scems to me highly probable that when the chromatic aberration is SO far corrected that the eye can distinguish no colour, sutIicient colour, unappre- ciahle by the eye, may still remain t o render invisible such objects as are extremely faint, and that in this way tele- ecopes of otherwise disproportioiiatc power may he brought to a level when the light to be discerned is extremely fceble: thus, in the case before us, the largest telescopes employed

*) In testing in this respect the goodnefs of a telescope the readiest method is to apply a high magnifying power, and then project the image of a star seen with one eye npon a serics of small concentric circles drawn upon a card and seen with the other eye.

in searching for Hnlley’s comet were not made by Fraun- hofer, yet iu ihe order or discovery his stand first.

The probability above mentioned adniils sonle degree O €

proof, perhaps all of which such a subject is susceptible. Sir ZVilliam Herschels beautiful A’e wtonians of 6,3 inches aperture and 7 feet focal length were considered, I believe, by himself and generally by otliers as equivalent to DolZoonds celebrated treble oljject glafs refractors of 46 inches focal length and 3,6 inchcs aperture. Yet when the same celestial body appears equally luminous in both, when tlie same faint double star is barely perceptilde but equally well defined i n both, a faint nebula will be visible iu the reflector which the refractor will not show.

In certain respects only can its exhibition of double stars be regarded a9 the test of the gooclnefs of an acbrornatic ie- lescope; its power of showing very faint ncbulw is perliaps a siirer test; Imt it doth not follow that because a telescope displays one of t h e objects well, ii will of necessity ex- hihit the other. The french glals, SO far as I have seen it, is strongly iiiiteCI; Frnunhofers is coloiirlel’s; hokv Tar this may have influenced the pliaenornenori \vhich hat11 given rise to this letter canriot be dcterminctl, Iiul I am disposed to attribute i t to a diEerent cause, wli ich is, that wliat iiiay be designated the inappreciable colour, or colour of which the presence can be ascertained only by its efrcctc, is inore fully corrected in Pmunh0fw.s tLan in a n y other inslrumellts, a result rather of his mechanical skill t l ian of tlie superiority of his materials (excellent as they ul:qiicstionably are), of his having preferred applying I h e certain prinrip!es of Science to what is called working by hand; and i t is to the degree in which this by the eye inappreciable chromatic aberratioI1 is corrected, that , czteris paribus, I would ascribe the sI1

periority of any telescope.

Nachrichten, me learn that in a 3,s achromatic by WoZZond, (I believe one of the celehrated 46 iiicti telescopes above al- luded lo) Iialley’s coniet was seen but one day later than with the large one he liad employed, a circutiislance, which, considering i he smallaefs of its aperture, will prove this in-

Datum. - 1835 Jgnrier 5.

Ziam Herschel when speaclriiig of the sixth and seventh satel- lites of Saturn havitig been found with his Forty feet reflector but then seen with one of tweiily, may be appropriately introduced, ,,it should be remembered that when an object is ,, oncediscovered by a superior power, an inferior one will su5ce

6.

x m e r Anzahl

der Faden. -rv

5 5 5 5 5 5 4 5 5 5

5 5 1 5 5 5 5 3 5 5 5 5 4 2 4 5

5 5 5

5

5

7 .

Sterawartc in1 Jahre 1535 hcobac

Datum. Gestirue. - -- 1835 April 8. 77kCancri

seq. - Moiirl 1 30 g Leonis 41 y Leonis

9. 30 7 Leonis 41 y h u n i s 3lonti 1 46 i Leonis 63 x Leonis

30 g LeoIiis ,13 Leonis

9. 15 g Virginis 29 yf Virginiy Mond I 51 6 V-irginis 67 cr Virginis

Juni 6. 51 4 Virginis hIond I 82 IU Virginis

7. 82 ni Virginis hIontl I 2 a Iibrae 13 $’ Librae

8. 2xLilirae i5g‘Librae

44 7 Librae 46 4 Librae

I 9. 44 Lihrae

nlai 6 . Mord I

m i d I

9.

3 5 5 3 5 5 2 5 5 5 5 5 5 5 4 5 5

23.

Febrnar9.

46 4 Lilwae JIontl I 9 w Ophiiichi 35 n Ophiuchi

10. 9wOpbiuchi 35 7 Ophiiiclii Nond C - It 46Sagiltarii f3,u’Yagittarii

Juli 6. 38yLibrae Mond I 8 Scorpii 21 o( Scorpii

Mond I 10a Capricorni

August 6. 41 xsagitlarii

10.

12.

13.

Spril i.

Moudsteriic auf cler CI Gestirne.

30 r l’iscirim 33 sl’iscium Mond I 20 111 Ceii 20 in Ccti nIolld I 98 p. I’icciuni 106 v L’isciiim 98 p PiPCinin 106 v l’iscium Rlond I 65 g’ Celi 73 k2 Ceti 91 ACeti i\.lond t 35 ATauri 37 A’ Tauri 46 4Librae 7 6 Scorpii R.Iontl11 1 1-1 Geminorurn 7 7 Geminorurn JIOIILI 1 43 ( Geminorurn 55 GGeininornm 43 (Geiniriorum 55 6 Geminorurn BIond I 78 /3 Geiiiinorum 83 @ Geminorurn 69 L, Geminorurn 78 /3 Geminorurn Mond I $3 yCancri 47 6 Cancri 4ALeonis blond I 41 y Leonis 47 p Leonis 41 y h o r l i s 47 p Leonis Blond 1 78 LLeonis 2 $’ Virginis 83 Cp Geminorum 6 Cancri Mond I 77 Cancri

-ry

Scheinbnrc AR. -- 231153’ 2S”8Y 23 56 52,21 0 f 1 3,T4 0 44 33,94 0 44 33,91 0 55 37911 I 21 32,35 I 32 50,41 I 21 32714 I 32 50,47 1 39 54,31 2 4 15,28 2 19 23,35 2 50 52,73

3 5 1 33,03 3 54 57,06

15 44 25,59 I 5 50 34,55

3 11 53,05

16 14 31929 5 54 5,57 6 4 55241 6 21 41,83

7 10 15,80 6 54 19,67 7 10 16,28

7 35 13,18 7 43 23,96 7 25 45,15 7 35 12,66 7 52 26,6S 8 33 44,20 8 35 18,66

9 51 0,26

10 24 7,86 10 10 52,83 10 24 7,47 1 0 48 43,62 11 15 20,32 11 36 47,61

7 43 23,51

6 25 3,67 8 59 52,11

6 54 19762

7 21 11,74

9 22 18,55

10 10 52,96

7 53 2 2 4 5

:litet.

Sclieinbare AR. ‘-

8 59 52,06 9 0 51,88 9 22 50,87 9 58 20J2 10 10 52,65 9 58 20,23

I 0 10 52,64 10 19 51,Ol 10 23 23945 10 56 31,02

9 55 47,75 9 58 19,90 11 40 39,09 12 I 1 28,bO 1 2 33 10,34 12 3s 59778 13 1 25,75 13 16 31,62 13 1 20,44 13 9 4,36 13 32 58,68 1 3 32 5Y,G5 14 4 18,11 14 41 47,2% 14 47 50,85 14 41 47,22 1 4 47 51,02 15 2 45,82 15 34 49,9l 15 44 28,?8 15 34 49,66

16 5 11,19 16 22 23,77

1 6 22 2?,62 17 0 5i,12 17 11 19,04 17 13 51,lP 1 7 49 45,40 18 3 55,77 15 26 20,03 15 36 48,57 15 5 5 53,06 16 19 20,25 18 59 59,28 19 30 23,81 20 17 54,58

15 44 28,03

17 0 57917

AnzahI der Faden. Lh-

5 5 3 5 5 4 5 5 5 5 5 4 2 5 4 5 4 5 4 5 5 5 5 3 5 3 4 5 5 5 5 5 5 5 5 5 2 5 5 5 5 5 5 5 4 5 5 4