February 20, 1896] 



NATURE 



367 



A lady who had lived in India mentioned, in this connection, 

 that she had often noticed natives, after taking up a photograph 

 to look at it, replace it upside down. One of those two boys, 

 looking at pictures, preferred to hold them upside down. 



A. B. M. 



Lecture Experiment on the Nodes of a Bell. 



Referring to Mr. Taylor's letter on the above subject 

 (January 23), the method he describes requires, in the first place, 

 a belljar of very wide edge — at least half an inch — and the re- 

 sult, when obtained, would only be visible to one or two persons 

 at a time. May I suggest the following method, although, very 

 probably, by no means new. 



An ordinary bell-jar with a plain edge (not welted) is fixed 

 firmly in an inverted position ; from a metal ring, arranged above 

 It, are suspended eight small beads by fine threads, in such a 

 manner that they rest lightly against the outside of the edge of 

 the jar. It is convenient (though not necessary) to so arrange 

 the beads that they touch the circle of the jar at equidistant 

 points. On then bowing, the beads are all jerked out from their 

 positions, and can be heard rattling against the glass as they fall 

 back ; and it is easy to note that at the nodes the disturbance is 

 comparatively slight, while it is more violent in the ventral 

 segments. H. G. WILLIAMS. 



Middle School, Ipswich. 



T 



THE PLANET VENUS. 

 HE planet Venus, as every observer knows. 



difficult and, at the same time, a tantalising object 

 for observation, for when she is in that part of her orbit 

 nearer to us, and therefore greatest in size, she presents 

 us with only a small illuminated crescent, from which it 

 is impossible to gather much from her surface markings 

 as a whole. Although at her greatest distance from us 

 she presents her whole disc, yet the latter appears so 

 small that even in this case satisfactory observation is 

 not obtainable. We have to content ourselves, therefore, 

 with observations made between these two stages, and 

 Avhen her apparent disc is thus semi-illuminated. 



That such an important question as the time of rotation 

 •of the planet about her axis is not yet definitely settled, 

 is quite sufficient to indicate that the observer has not 

 ■everything his own way. 



In a former number of N.MURK (vol. xlvi. p. 469), a 

 ■summary was given of the valuable observations made 

 "by the late M. Trouvelot at Cambridge, United States, and 

 Meudon, extending over the years 1877- 1891. The chief 

 points to which reference there was made were the two 

 kinds of spots, white and grey, one specially prominent in 

 size having appeared on September 3, 1876 ; the snow 

 caps at the poles, and the bright specks which appeared 

 at their southern extremities ; the varying shape of the 

 terminator, which occurred sometimes in the space 

 of a few hours ; and, finally, the period of rotation. 

 Trouvelot found that the whitish and greyish spots 

 were very difficult to observe, even under favourable con- 

 ditions. The former were situated near the terminator, 

 and produced on it slight deformations, which seemed so 

 to alter it as to suggest that these spots are at a higher 

 level than the other parts. The greyish spots, on the 

 other hand, when situated in about the same positions, 

 also deformed the terminator to a small extent, but in an 

 opposite way to those just mentioned, suggesting that 

 these spots he at a lower level than the parts near them. 

 Another peculiarity of these two kinds of spots which he 

 remarked was their size. The white ones seemed to assume 

 a round or slightly oval form, and were nearly always 

 small, while the grey spots were generally of an elongated 

 shape and of large dimensions, forming sometimes straight 

 bands. That the spots were not necessarily of long 

 duration was also remarked, and they were analogous in 

 their formation to " taches des couches nuages continues 

 de notre atmosphere pr^cddant les pluies, et qu'un 

 simple jeu de lumi5re fait naitre ou disparaitre." Their 



NO. 1373, VOL. 53] 



contours were described as very vague, those of the white 

 spots being less brilliant, and those of the grey spots less 

 dark. 



In the observations that were made at the Catania 

 Observatory and at Mount Etna {Astr. Nach., Bd. 139, 

 No. 3329), and to which a brief reference is here made, 

 the observer, Sig. A. Mascari, describes in detail the 

 appearances of the spots during the years 1892- 1895. 

 He also differentiates between the two kinds of spots. 

 " Le macchie oscure si presentano ordinariamente sotto 

 forma di leggiere velature grigie a contorni mai netti, 

 molto deboli, senza alcun limite deciso, ed h assai raro e 

 fortunato quel momento in cui gi puo arrivareadistinguere 

 con precisione qualche contorno netto." The second 

 type, " Le macchie chiare si rilevano per un maggiore 

 splendore rispetto a quello del resto del pianeta. 



Fig. I. — October 12, 1892. 



F^rom the series of twenty drawings which accompany 

 the observations in the communication referred to above, 

 the surface markings can be clearly followed. 



Fig. I, which is one of a series of four drawings made 

 in the months of October and November 1892, gives the 

 general appearance of the surface as it was then observed. 

 The three dark patches, A, B, and C, were nearly always 

 visible ; a was not always so prominent as is shown in 

 the drawing. The terminator was also at times irregular 

 in shape, being specially so on November 14. The edge 

 of the south polar cap, near the terminator on October 

 13, assumed a somewhat similar appearance to that which 

 Trouvelot recorded on September 27, 1876. The obser- 

 vations of the latter indicated that the most striking 



Fig. 2.— September 25, 1893. 



irregularities were found at the extremities of the ter- 

 minator close to the edge of the pole-caps, where deep 

 notches were often recorded. They were of different sizes 

 and shapes, and underwent rapid changes in periods of 

 sometimes a few hours. These facts led Trouvelot to 

 believe in a short period for the rotation of the planet. 

 In the observations for 1893, the terminator was directed 

 towards the east. 



Fig. 2 shows the planet for September 25, 1893, i^om 

 I3h. 50m. to i4h. 52m. The bright spot, H, is bounded 

 on the east and west sides by dark, well-defined contours, 

 r,/, and ;//. The region about c was somewhat obscure ; 

 the area enclosed by /, /;/, tt was bright and sometimes 

 circular, being bounded, for the most part, by dark in- 

 distinct contour lines. 



