NEWTON'S OBSERVATION OF EGRESS, AT MOKATTAM. 295 



OBSERVATION of the EGRESS of VENUS, 1874, December 8, by 



Mr. F. M. NEWTON. 



Mr. Newton was indebted to the kindness of Mr. WARREN DE LA RUE for 

 the use of a fine Equatorial by Dallmeyer of 4| inches aperture, driven by 

 clockwork, and fitted with a solar diagonal reflecting prism. This instru- 

 ment was mounted in the hut with revolving roof sent from England for the 

 Altazimuth. The Secondary Sidereal Clock Dent 2015 was also mounted 

 within the hut, and was used by Mr. Newton ; its comparisons with the 

 transit-clock are given on the preceding page. 



For the observation of the Internal contact, Miss Newton used an achro- 

 matic of 3 inches aperture, the property of her brother, temporarily mounted 

 on a rough equatorial stand, constructed of wood. The Sun was viewed 

 directly, that is, without the intervention of a reflector. 



Mr. Newton writes to the Astronomer Royal from Mokattam Heights, 1874, 

 December 7 : 



" I take the liberty of sending you a drawing of Venus [Plate X., Fig. 6] 

 taken with Mr. De la Rue's exquisite telescope on Saturday, 5th, at l h , showing 



that the crescent is now considerably more than a semicircle.* 



I thought it would be well to note, before the transit occurs, an appearance 

 which seems to point to an atmosphere on Venus, which may make the 

 phasnomena of the black drop in the real transit rather different from those in 

 the Model transit. The power used in making the drawing was 300 diameters." 



" Account of Impressions during the Egress of Venus, 1874, December 8. 



" The clouds broke at 12 h . 9 m . 4 s . I was using a reflecting solar eye-piece 

 with power 145, and saw Venus at intervals. Finding the clouds continuous, 

 I put in an eye-piece magnifying only 52 diameters, and after observing with 

 it a few minutes, I removed the dark glass and observed the image projected 

 on a sheet of paper, in which the diameter of Venus was about f ths of an 

 inch. I thought that very good observations could be made in this manner. f 



" The weather improving I replaced the eye-piece of 145. Light clouds 

 obscured the Sun at intervals, and the limb was " boiling " considerably. 

 About 10 minutes before contact a thick cloud swept over the Sun, completely 

 obscuring it. This, happily, cleared off about 10 seconds before contact, 

 leaving the Sun fairly but not well defined, owing to a slight haze following 

 the cloud. The contact was observed through this at 13 h . 22 m . 20 S> 7 by the 



* In Mr. Newton's original sketch the bright cusps are 143 apart ; in other words, the crescent is 

 37 more than a semicircle. 



f This method was employed by the members of the Mexican Expedition to Japan. 



