470 



NA TURE 



(_September 15, 1892 



such observations as these has been found to be con- 

 siderably studded not only with small, but with great 

 differences of configuration, the terminator varying greatly 

 in many phases of the planet. M. Trouvelot's results 



Fig. 7.— Showing irregularity of Terminator, November 2j, 1877. 



show that these deformations become most apparent 

 when Venus is at her greatest eastern and western elon- 

 gations. Sometimes one half of the terminator is seen 

 concave, while at the same time the other is convex 



(Fig. 7) ; small indentations at the horns (Fig. 8) also 

 seem to be of common occurrence, and occasionally the 

 curve of the terminator is perfect, no trace of any irregu- 

 larity being noticed. Not only then does the terminator 



^^ 



Fig. 9. — Febru.ary 5, 



2h. 



Fig. 10. — February 5, 

 Sh. 43m. 



change in form, but changes are found to occur very 

 rapidly in intervals of only a few hours. To take one 

 case out of many, we may quote the instance recorded 

 in 1 88 1 on February 5 at 2 p.m. (Figs. 9 and 10). At 

 NO. T 194, VOL. 46] 



this time the terminator appeared as a straight line 

 showing Venus then in apparent quadrature, but at 

 5h. 43m. this line was quite gibbous, and its curve regular. 

 A very important point about the repetitions of the same 

 deformations is that they do not occur at exactly the 

 same time each day, but appear to change the hour of 

 observation, " the periodicity of these phenomena, if 

 periodicity there is, not being exactly twenty-four hours." 

 From a long series of observations, the most striking 

 irregularities were found at the extremities of the ter- 



FlG. II. — Showing the shape of the horns, September 27, 1876. 



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

 niches were often recorded. These indentations were 

 noticed to be generally of different sizes and shapes, some- 

 times the north one being larger than the southern one, 

 and vice versa. They also underwent very rapid changes 

 even in the space of a few hours, a case occurring on 

 September 27, 1876 (Fig. 11). "At one time the extremity 

 of one of the horns would be more or less truncated, 

 when the other would be sharp, and some hours later the 



An abnormal exttnt of the crescent, May 13, 



reverse would be the case, that which was sharp being 

 truncated, and that which was truncated being sharp." 

 M. Trouvelot concludes that his observations bring out 

 a very important fact — " qu'il a une relation tr^s ^troite 

 entre les deformations les plus importants subies par le 

 terminateur et paries cornes, et les taches polaires de la 

 planete " 



When Venus approaches inferior conjunction with the 

 sun, its crescent gradually diminishes until the illuminated 

 surface is turned exactly away from us. Just before this 

 position is reached, the crescent has been found to present 



