( 1<)9 ) 



I have been able to use the telescope for observing, at least partly, 

 the transit of Mercury on November 14 1907, and I venture to 

 publish my results here. 



To give my telescope a firm basis I had a pier built of beton 

 surrounded by an isolated floor and provided with a movable roof 

 open at the sides, which roof can be entirely moved aside. For the 

 transit of Mercury, however, I kept the roof over the instrument in 

 order to protect myself from the burning sunbeams and especially 

 to keep out the 'light from outside as much as possible. 



For the observations I had constructed a projection apparatus, a 

 kind of camera having the shape of a truncated pyramid, of which 

 one side is open and the three others are coated with black paper. 

 The base on which the image was to be formed was at a distance 

 of about 14 cm. from the eye piece. The camera was adjustable in 

 distance and in inclination, to secure the proper position of the 

 plane of the image. 



With the highest power of the telescopa, 133, the diameter of 

 the projected image of Mercury was nearly 1 mm. The fine solar 

 spots that were present could be sharply observed and those in the 

 neighbourhood of the western limb could be seen surrounded by 

 very distinct faculae. 



Unfortunately the beginning of the transit was hidden from mv 



view by clouds. Towards 1 o'clock mean time of Chiloango it began 



to clear up and, after Mercury had been visible on the sun as a 



well defined disc, its egress could be observed very well. I found: 



third contact at 2'>35 m 38 s M.T. Chiloango 



last „ „ 2 38 7 „ 



The moment of the 4 th contact, that at which the last impression on 

 the limb seemed to disappear, was difficult to estimate within some 

 seconds chiefly owing to the unsteadiness of the images, but I hold that 

 but for this unsteadiness the observation of the last internal contact 

 could have been made with great precision. The corrections of my 

 chronometers were derived from time determinations before and after 

 the transit. 



The times computed from the Nautical Almanac for the 3 rd and 

 the 4 !l ' contact at Chiloango were 2''35 m 47 s and 2''38 m 24 s . Thence 

 follow for the differences observation — computation: — 9 s and — 17 s . 1 ) 



l ) (Note added by E. V. v. d. Sande Bakhuyzen). According to the mean of the 

 observations made at Leiden, these differences were — 6 s and — 21 s . Hence the 

 results of Mr. Sanders agree very well with these. The greater difference for the 

 4th contact must probably be ascribed to the circumstance that all the observers have 

 observed this phenomenon too early. 



