Captain Kater’s floating collimator , &c. 309 
doing it not imparted at the same time, astronomers would 
have received it as one of the most important discoveries of 
modern times in this science, and anxiously expected its 
details. 
What I have adduced in these tables of observations, will, 
I hope, assist in enabling others to appreciate the value of 
this new astronomical power, which, unless I deceive myself, 
may be considered as even belonging to a future more ad™ 
vanced state of practical astronomy. 
Explanation of, and remarks on Table I. 
The index corrections used in obtaining these results were 
found by the collimator. The zenith distances of the inter- 
section of the wires of the collimator were found in the north 
and south positions. Half the sum of these is the inclination 
of the line of collimation of the collimator, and half the dif- 
ference is the index correction. A mean of the index correc- 
tions, as determined on several days, has been used. This is 
not exactly the method suggested by Captain Kater ; but 
the mean results must, in effect, be the same as if the correc- 
tion had been determined for each observation. In making 
many observations with a large instrument, it would not be 
convenient, or perhaps advisable, to make for every star ob- 
served two cotemporaneous observations with the collimator. 
In this manner, however, a greater consistency in the sepa- 
rate results might be expected ; but, as far as I have exa- 
mined, there is no very marked superiority. That a judgment 
may be had, in three instances marked S, the results are de- 
duced in this way ; and certainly the agreement between the 
zenith distances of each day appears somewhat greater, than 
MDCCCXXVI. S S 
