128 



The Rev. Dr. Robinson on the Difference of Longitude 



southern window of the transit room. I had intended to use my great reflector, 

 with a power of 70, but the rapid motion of the rockets across the field* of view, 

 and the oblique movements of the equatorial, 2". 1 5". from the meridian embar- 

 rassed me, and after losing a few, I betook myself to its finder, 2|'° aperture, 

 power 18, with a field of 1|^ degrees, which proved quite satisfactory. The 

 clock is by Sharp, with a mercurial pendulum. Mr. Robert Finlay (F) was to 

 observe with Troughton's equatorial, 2|'" aperture, power 75, but as the field 

 of view is narrow, and from not being accustomed to such instruments, he was 

 even more embarrassed than I ; he also was driven to the finder, which is a com- 

 mon affair, with an aperture of an inch. The clock has a gridiron pendulum. 



The equatorial clocks were compared with the transit clock by chronometers, 

 before and after the observations of each night ; and as the simple reduction of 

 these indications to sidereal time is not likely to involve any mistake, the obser- 

 vations are given in sidereal time, as it seems needless to occupy valuable space 

 by setting down the actual clock times noted. They are as follow : 



May 14, 1839, cloudy, high wind, fourteen rockets fired. 



ARMAGH. DUBLIN. 



_, |-Seen, but not observed. , . . . 



No. 2. R 

 E 



} 



Seen. 



No. 3. R Seen. 



E 13*. SG". 24'. 68 



H 13\ 37". 39'. 10 



E observed with the naked eye. 

 No. 4. R1 

 E 



No. 5. R 

 E 



}Seen. 

 iDitto. 



H . 42"". 32'. 10 

 H . 48 25 10 



* They rose, on an average, a degree of declination above the boundary of view, while the field 

 is but 38 minutes. 



