Changes that happen to the jixed Stars. 171 
well distinguished from 3m. 2.3m, however, cannot be suf- 
ficiently kept apart from 3.2m, or either of these expressions 
from 3m, or from 2m. Perhaps the former may be dis- 
tinguished from 3.4, and the latter from 4m. 
The following step from 3m to 4m, or indeed from 3.4m to 
4.5m, is less decisive than from 2 to 3m. 
Again, if a star had changed from 4m to 5m, or from 4.5m 
to 5.6m since Flamsteed's time, we could hardly entertain 
more than a very slight suspicion of the alteration. From 4 
to 5.6m, or from 4.5 to 6m, would be a pretty considerable 
step, and might serve as a foundation for an argument. 
A change from 5m to 6m is such as no stress could be laid 
upon ; and such are the changes from 5.6 to 6.7m, and from 
6 to 7m. In all these inferior orders less than an alteration 
of a magnitude and an half could hardly deserve attention. 
Here we have supposed all references to be made to the 
same author ; for when other astronomers are consulted the 
uncertainty is much increased. A star which in Flamsteed's 
catalogue stands 12m, may be found 2m in another author: 
2m in the former may be rated 2.3m, or even 3m by the latter. 
Of course 3m and 4m may be written for the magnitude of 
the same star by different persons. 4 and 5m as well as 5 
and 6m are frequently interchanged, and no stress can be laid 
upon such nominal differences in different catalogues. We 
can hardly allow less than half a magnitude in the higher 
orders, and a whole one in the inferior classes, for this uncer- 
tainty. 
To apply what has been said : suppose there should be some 
inducement to believe a certain star, such as (2 Leonis, to have 
changed its lustre. Now having no real, existing type of 
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