378 ASTRONOMICAL OBSERVATIONS MADE AT [47 



The values of the correction for different values of / and A are given 

 in Table IV. at the end of this Introduction. 



Correction for Change of Declination. 



In the case of the Sun and Planets a small correction is required 

 for the motion in Declination in the interval between the time of crossing 

 the meridian and the time of observation. 



This interval is IG'-fi/cosec A, 



where / has the same signification as before, and therefore the correction will be 



- Jcosec A x Var. of Decl". in 1 hour of longitude. 

 3600 



The last factor is obtained from an Ephemeris. 



The multiplier of / in this expression, or the value of the correction 

 for one interval, is given by means of Table V. at the end of this 

 Introduction, so that the correction may be deduced by multiplying the 

 number taken from the Table by /, the number of intervals stated in 

 the eleventh column. The sign to be given to the correction is stated 

 in the precept at the foot of the Table. 



The Micrometer-wire was always so nearly adjusted equatorially that 

 no correction for error of its position has been thought necessary. 



The Pointer, which is used for setting the Telescope to observe an 

 object either directly or by reflection, the setting angle to the nearest 

 minute having been previously computed, is placed below Microscope A at 

 an interval of 10 45' nearly from the zero of its reading. The graduation 

 proceeding in the direction from the microscope downwards, the Pointer 

 reading is the number of degrees and minutes of that division which in 

 the order of graduation comes next before the position of the Pointer. 



It is unnecessary to place the Pointer reading in a separate column, 

 as it may be at once inferred from the concluded Circle reading, the 

 minutes being always an integral number of 5'. 



The concluded Circle reading in the twelfth column is the Pointer 

 reading added to the mean of the Microscope readings with all the above- 

 mentioned corrections applied. It is therefore the reading which would 

 have been given by the Circle, if the microscopes had been in accurate 

 adjustment for runs, and the object had been bisected by the fixed wire 



