160 



Intelligence and Miscellaneous Articles. 



The ring was distinctly seen when the aperture was reduced to one 

 and a half inch. The 9-inch equatorial could not be used, as there 

 were no means of excluding the direct sunlight. 



The morning after the transit the sky was slightly hazy, and the 

 planet could not be found, though probably it might have been if 

 the small telescope had been mounted equatorially. 



On the day following (the 10th), the crescent, extending to more 

 than three fourths of a circle, was seen with beautiful distinctness 

 in the equatorial ; and on this and two subsequent days, measure- 

 ments were taken with the filar micrometer for the purpose of de- 

 termining the extent of the cusps, and consequently the horizontal 

 refraction of the atmosphere of the planet, on the assumption that 

 the extension of the crescent and formation of the ring are due to 

 this refraction. 



The results of these observations are given below, each result 

 being the mean of the number of separate measurements indicated 

 in the last column. On the 10th, the chord of the arc between the 

 cusps was measured • on the-other days the distance between lines 

 tangent to the cusps and to the opposite limb. 



Mean dates. 



Distance of 



centres of Sun 



and Venus. 



Extent of 

 Crescent. 



Horizontal 

 refraction of 

 Venus's atm. 



Number of 



observations 



of cusps. 



h m 

 Dec. 8... 3 Op.m. 

 „ 10.. .11 36a.m. 

 „ 11... 10 16 a.m. 

 „ 11... 2 40p.m. 

 „ 12... 2 45p.m. 



36-6 

 2 31-7 

 4 2-5 



4 20-4 



5 58-3 



360 

 279 28 

 233 15 

 231 46 

 215 21 



Mean... 



46-6 

 430 

 45-5 

 42-9 



44-5 



4 

 6 



15 



22 



These observations give a mean of 44'-5 as the horizontal refrac- 

 tion of Venus's atmosphere, or about one quarter greater than that 

 of the earth's. The writer's observations in 1866 gave.45'*3. 

 Madler, from observations of the cusps in 1849, when the nearest 

 approach of the planet to the sun was 3° 26', made the refraction 

 43'-7. 



The formula for the refraction is this : 



sini/=sinc?sin 



e-180 



2a?=y- 



in which cl= distance of centres of Sun and Venus. 



c=arc of crescent. 



r= Sun's semidiameter. 



o= radius vector* of Venus. 



#=horizontal refraction of Venus's atmosphere. 

 Six measurements of the diameter of the planet on the 10th 

 give 63"-l. Twenty-four on the 11th give 63"-75. The English 

 and American Almanacs give 62"-4 and 64" -5 respectively. — 

 Silliman's American Journal, January 1875. 



