Dkc. 8, 1882.] 



• KNOWLEDGE 



453 



edges of the two discs, and the observer would only have 

 to note that instant ; while, when Venus was leaving the 

 sun, he would only have to notice the instant when the fine 

 thread of light was suddenly divided by a dark point. But 

 unfortunately Venus does not behave in this way — at least, 

 not always. With a very powerful and very excellent 

 telescope, in perfectly calm, clear weather, and with the 

 sun high above the horizon, she probably behaves much as 

 Halley and Delisle expected. But under less favourable 

 conditions, she presents at the moment of entry or exit 

 some such appearance as is shown in Figs. 'J and 10, 

 while with a very low sun she assumes all sorts of shapes, 

 continually changing, being for one moment, perhaps, as 

 in one or other of Figs. 9 or 10, and in the next dis- 

 torted into some such pleasing shape as is pictured in 

 Fig. 11. 



Fig. 10, 



Accordingly, many astronomers are disposed to regard 

 both Halley's method and Delisle's as obsolete, and to 

 place reliance on the simple method of direct observation 

 first described. They would, however, of course, bring to 

 their aid all the ingenious devices of modern astronomical 

 observation in order to overcome the difficulties inherent 

 in that method. One of the contrivances naturally sug- 

 gested to meet such difficulties is to photograph the sun 

 with Venus upon his face. The American astronomers, 

 in particular, consider that the photographic results ob- 

 tained during the transit of 1874 will outweigh those 

 obtained by all the other methods. European astronomers 

 failed so thoroughly with this method in 1874 that they 

 place no reliance on it whatsoever. 



•»>• COMET'S PATH. 



"ITTE have to give this week the comet's path (both 

 V T pictures) again, a strange mistake (though easily 

 explained) having crept into the maps given last week. 

 The path, deduced from Chandler's estimates was, through 

 a misunderstood instruction from the Editor, who was 

 away from town, thrown twenty minutes eastward, and 

 thus a much more marked discrepancy than actually exists 

 between ^Mr. Hind's and Prof. Chandler's results was made 

 to appear staringly on the maps. Those now given are 

 correct. The dates from the small map are as follows : — 



Ebkati'h. — DoLLONii'.s 3-iKcu "Student's" Tblesiope.— We bcR 

 to correct the following compositor's error which appeared in your 

 laat issue under tlie heading of " Extracts fi-om letters respeetiiijf 

 the Student's Telescope," namely •—" 3. With power ICO, JDrsjv 

 Majoris " shoidd have been " SUrsa; Majoris." — The latter is a 

 difficnit test, while the former is an easy one, and may mislead. — 

 DOLLOKD & Co. 



mHbi 



