( 468 ) 
Magnitude of the artificial star Eh 12 8m6 9m5 
Personal error at the appearance 08,275 08,316 08,413 05,530 
disappearance 08,314 08,329 08,387 08,489 
” ” ” ”„ 
It is obvious that the absolute value of this personal error depends 
not only on the observer, but also on the apparatus and on the 
observing method. The differences of the personal error resulting from 
the different degrees of brightness are neither influenced by the 
apparatus nor by the observing method. As care has been taken 
that the observations with different magnitudes should be made 
in rapid succession and that they should be distributed symmetri- 
cally, the variations of the personal error with brightness may be 
deduced from the numbers given above with tolerable accuracy. 
In the “Archives Néerlandaises” I have derived from these results 
an explanation of the relation between the personal error in the 
transit observations of stars and their brightness. Here I shall only 
refer to the influence of this error on astronomical observations in 
which the sudden appearance or disappearance of a star must be 
determined, as for instance with a ring or bar micrometer. In 
determining the differences of right ascension of small and bright 
stars systematical errors of more than 08.2 may occur; a good 
example is seen in the series of observations of O. A. L. Prmr to 
determine the positions of stars in the stellar cluster of y Persei, 
(The stellar cluster 7 Persei micrometrically surveyed, 1891) where 
the errors amount to more than a second of time. 
This personal error will have a great influence on the position 
of the moon derived from the observations of occultations. The amount 
of the error with different methods of observation (registering method, 
eye and ear method) may obviously vary; it seems, however, that 
this error does not differ much for the appearance and the dis- 
appearance, so that the influence on the moon’s diameter will not 
be great, wheras the moon’s longitude, derived from occultations 
especially of smaller stars will be too large and its error may 
amount to 0”.2 and more; therefore it is necessary to determine 
this error and to account for it. 
