17 



viz. ü)i the centre and on two points on either side, one abont half- 

 way iietween the middle and tlie extreme vertical wire, and another 

 just l)eyond the latter. In this manner the following corrections were 

 deduced, to be appUed to the declinations deduced from pointings at 

 these points : 



Clamp West wire a : — 0".12 -f 0".15 0".00 — 0".ll — 0".33 



wire b: — 0".67 0".00 0".00 + 0".04 — 0".08 



The [)oinls are given in order, starting from the side of the clamp. 



The first and third pointing on the south-limb of the moon were 

 made on wire a, the second on wire b. The following corrections 

 to be applied to tiie zenith-distance were computed: -j-f*."17 — 0".02 

 + 0"41. 



On the ground of a number of nadir-delerminations 6".43 was 

 found as representing half the distance of the two horizontal wires. 

 The refraction was calculated from tables in manuscript which are 

 used in the observatory ; these are l)ased on Besskl's constant and 

 Radau's theory. From observations made at tlie observatory it appears 

 that this refraction has to be diminished iiy 0.2 "'„, and this correction 

 has therefore been applied. 



Foi' the mean latitude of Leiden I have taken as (he most probable 

 value 52°9'iy".80. The correction for the motion of (he pole was 

 deduced from the papei' i>y Ai.brkcht (A. N. 4749) for a moment 

 1.2 of a year prior to the eclipse; in tiiis manner account was 

 taken of the J4-monthly motion, but an error is introduced 

 in the annual term. This error, however, seemed unimportant and 

 in tills way I found Ay r= -|- 0".09 ') and therefore for the iustaii- 

 tanious latitude 52°9'19".89; this value') was used in the reductions. 



In order to pass from the observed declination of the limb to 

 Ihnt of the ceiide of the moon 1 have taken into account the irre- 

 gularities of the liml), which were very distinctly visible as the dark 

 disc of the moon was jirojected on the bright disc of the sun. Using 

 the profile given by Hay.n (A. N. 4724) I have made a drawing of 

 the part of the limb which was visible in (he telescope and by (he 

 aid of notes, taken down during the observation, about the manner 

 in which the pointings had been made, the corrections were estimated 

 which had to l)e applied to the declinations as reduced \\ i(h a mean 

 radius of the moon ; these corrections came to — 0".7(), — 1".9(), 



1) Dr. ZwiERs from a pi-eliminary discussion of tlie latest results for the uiotioii 

 of the polo, in continuation of his paper in these Proceedings for 1911, finds 

 ;i»=-t-0". 14 (however not including the z-term). 



-) Fioin the preliminary results of Albrecht (A. N. 4802) for the variation of 

 latitude in the year 1914 I find a¥' = +0".20 (added June 1915). 



2 



Proceedings Royal Acad. Amsterdam. Vol. XVIII. 



