84 ® Capt. Kater’s experiments for determining the variation 
filled with sand, upon which a fiat stone was laid. But as 
this did not prove so steady as I expected, a larger stone was 
afterwards procured and laid upon the box, and upon this the 
transit was placed. 
The bell tent before mentioned was suspended over the 
transit from three spars lashed together at the top. 
The interval of time between the transits of the same star 
being all that is required for the present purpose, it is not 
necessary that the transit instrument should be accurately in 
the meridian ; it is sufficient that it should always describe 
the same vertical circle ; it was however brought very near 
the meridian, at all the stations, by the following method : 
The error of the chronometer was determined by altitudes 
of the sun, and the times were computed when the first and 
last limb would be on the meridian. 
The axis of the transit was carefully levelled, and a little 
before the time of the sun’s first limb coming to the meridian, 
the middle wire of the transit was brought in contact with it, 
and kept so by the horizontal adjustment till the calculated 
time of its arrival on the meridian. The position of the instru- 
ment was afterwards farther corrected if necessary by the 
transit of the second limb. At other of the stations, when 
the weather permitted, the instrument was brought extremely 
near the meridian by the transit of the pole star, the telescope 
being sufficiently powerful to command this star with eas6, at 
any time of the day. 
A mark (generally a flat board sharpened at one end to 
penetrate the ground) was sent to as great a distance as con- 
venient, and so placed by signal, that it was bisected by the 
middle wire of the transit ; and to this the instrument was 
