On the Transit Instrument in determining Latitude. 59 
Survey with the zenith telescope, as stated by the superintendent, 
shows that usually the latter error very much exceeds the former, 
or that the catalogues are less reliable than the instruments. The 
same is apparent from our own results. While the probable 
error of a single result (including both error of observation and 
of catalogue) amounts, on an average to + 0'°88, the probable 
_ error of observation, as distinct from that of catalogue, is found 
_ by comparing the repetitions on the same pairs in our first table, 
be only +048. 
A similar value of this error is given by 
_ & comparison of the longer series of repetitions on the last two 
ey twenty-one of the latter. The star-places used are 
of the English Nautical Almanac. 
“4 a Cygni and 61! Cephei and | 
Date of Obs. |*~¥Ey ni | Date of Obs. | 7. pheium, a 
_ 1859. | 58, Nov. 8 | 41° 18/ 41/2 —o!!5 
3 41° 18’ 42'h9 +0'"4 I 4t 4|—o +3 
4 42 ‘0 | —o °5 |] 75g, Ort. 15 42 °4| +0 °7 
7 4t *9| —O °7 18 42 +1 | 0 °4 
10 41 ‘9 | —0 ‘7 21 41 -3 | —o 4 
II 43 +7 | +1 :2 27 43 +2 | +1 ‘5 
15 41 -8|—o 8 29 fo: -8 | —o 9 
" 42 *7 | +40 *2 Nov. 1 42 0 | +0 ° 
21 42 +3 | —o °2 : 3 41 °4|—1 °3 
23 42 ‘9 | +0 ‘3 14 43 3 | +1 6 
25 42 2 | =o 4 15 go 6 | +r 
28 43 -6| +1 ‘0 23 42 -4| +0 6 
29 42 +8 oO °2 28 ar ibd 
Noy. 2 42 -8 pe . Deo: 8 43 0 | +1 °3 
3 43 -4 | +0 10 go -2|—r °5 
4 43 ‘o | +0 2 12 4r 6 | -—-o''T 
+) 43 :2| +0 °7 15 4t 0; —0 *7 
14 43 -0| +o -4 16 41 ‘9 | 40° °2 
17 41 -7|—o: 21 41.2 | -—0 5 
I 42 0 | —o 3 23 41 ‘6 | —o '1 
i 43 | Ses 24 41 x a 
ean 41 18 42°55 + oF 10 | Mean 41 18 417 of 12 
—Frob. Er. of single result + 0-471 7 oe 
Ds deemeithe eRe ii ee 
We have, then, for the probable accidental error of observation, 
from the repetitions on the same pairs in our first table, +048 ; 
from «and 61" Oygni, +0'°47; from 7 Cephei and w Piscium, 
055; from all these combined, +050. This ie a with the 
: e, +0’°88,. in 
of instrument and catalogues, in the present case, may be repre- 
rit to 7. That the Twelve 
and -£0’-80 for the other catalogues; although in the column for 
