368 



NA TUBE 



[February 20, 1896 



Fig. 3 shows this more clearly. This drawing, made 

 on October 13, seems to be more typical of the appear- 

 ance of the disc for this year. The six comparatively 

 large whitish spots, H, I, c;, N, M, L, are here clearly 

 shown. H is somewhat varied by an incursion of the 

 dark contour line on the east side ; I is also sometimes 

 partially bisected by a dark streak, as was the case on 

 Novemlaer 27, i6h. 50m. (Fig. 4). 



The different shapes which the terminator underwent 

 during this year's observation were very prominent, that 

 on November 27 being the most noticeable. 



The disc in March 1895, the terminator being directed 

 towards the east, presented the appearance shown in 

 Fig. 5. One can easily recognise the large white spots, 

 H, I, G, N, M ; I appears, however, no longer divided, 



while L seems to have more or less disappeared, giving 

 place to a prominent circular spot a little more to the 

 eastward. The detail observed during the months of 

 July and August can be best seen by examining Fig. 6, 

 which can be conveniently compared with Fig. 3 or 

 Fig. 4. 



With regard to the length of period of rotation of 

 this planet, the difficulties of identifying the spots after 

 brief intervals of time have rendered this point doubtful. 

 Leo Brenner on this point writes {Astr. Nachr., No 3300, 

 p. 197) : Obgleich ich bisher 107 Beobachtungen der 

 Venus zu verzeichnen habe, konnte ich doch erst 22 

 Zeichnungen anfertigen, weil die wahrgenommenen 

 Flecken gewohnlich so schwach und unbestimmt sind. 



Fig. 4. — November 27, 1893. 



dass ein gewissenhafter Beobachter Bedenken tragt, 

 ihre Wiedergabe zu versuchen, weil er fiirchten muss, 

 entweder ein Opfer von Selbsttauschung zu werden oder 

 die Ausdehnung der Flecke nicht richtig aufzufassen. 

 Deshalb halte ich auch die Berechnung der Rotation aus 

 Flecken, die so unbestimmt sind, fiir ganz und gar 

 unmoglich. Anders verhalt es sich aber mit Erschein- 

 ungen, welche so deutlich sind, dass sie ins Auge fallen 

 und iiber deren Wirklichkeit mithin kein Zweifel bestehen 

 kann." 



It is at present uncertain whether a rotation is performed 

 in, roughly, twenty-four hours, or whether it is accom- 

 plished in about 225 days. Trouvelot, from his numerous 

 observations, gave a period amounting to nearly twenty- 

 four hours ; while Schiaparelli still adheres to 225 days. 



NO. T373, VOL. 53] 



Quite lately also Tacchini, from observations made during 

 last summer at the Collegio Romano, favoured Schia- 

 parelli's view that the rotation period is equal to the 

 sidereal revolution ; and his observations {Atii Reale 

 Acad. JJncer, vol. v. p. 3) towards the end of 1895, have 

 led him to the same conclusion. The observations of 

 Mascari seem, however, to have led him to adopt the 

 longer of the two periods. Cerulli also, from observations 

 made in July, August, and November of last year i^As/r. 

 Nach., No. 3329) is inclined to adopt Schiaparelli's length 

 of period. Writing in Astr. Nachr. (No. 3310, p. 368), 

 he says : " Onde si conchiude che la configurazione delle 

 ombre di Venere si mantiene sensibilmente invariabile 

 per molts giorni, e non rivela nessun movimento con- 

 ciliabile con rotazioni di breve durata." 



"s^y^ 



Fig. 5. — March 23, 1895. 



Leo Brenner, on the other hand {Astr. Nach.^ No. 

 3314), is decidedly in favour of the shorter period, 

 and so is therefore of the same opinion as Trouvelot. 

 The former argues that if the spots preserve their positions, 

 then those near the terminator would be for some length 

 of time under the same conditions of illumination, and 

 therefore would appear the same. This he maintains is 

 not the case, and is not even borne out by the drawings • 

 of Schiaparelli and other observers. 



It may be remembered that Trouvelot determined his 

 value of 23h. 49m. 28s. from the observations of certain 

 spots, but he also stated that many of the general features 

 visible on the planet's surface, such as the rapid defor- 

 mations of the horns and of the terminator, &c., al 



I 



^ 



Fig. 6.— July 26 to August 5, 1895. 



suggested a short period of rotation, and were " incon- 

 ciliable avec la periode de rotation, si lente et si inattendue, 

 deduite par I'^minent astronomie de Milan." 



Brenner, who has observed Venus some 275 times, 

 says that the spots move with a velocity of I5°*030 in one 

 hour, thus indicating a period of 23h. 57m. 7"5459s. In 

 fact, he seems so convinced of the accuracy of his 

 observations, that he has published a map of the surface 

 of Venus, and finds that drawings by numerous observers 

 agree well with it. He maintains, also, that the dark 

 spots are true appendages on the planet's surface, and 

 are not connected with the cloudy atmosphere. (See 

 Astr. Nachr., No. 3300, p. 198, in which he refers to a 

 peculiar shaped spot situated near the South Pole, and a 

 communication from Stanley Williams. 



