-----+-------+-----+------+-----+------+------+-----+------
| sec | sec | sec | m s | m s| h m | sec | m s| m s
No. 1, | 1/160| 1/50 | 1/8 | 0 10 | 0 10| 0 2 | 1/6 | 0 1| 0 4
or f/4 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 2, | 1/80 | 1/25 | 1/4 | 0 20 | 0 20| 0 4 | 1/3 | 0 2| 0 8
or f/5.657 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 4, | 1/40 | 1/12 | 1/2 | 0 40 | 0 40| 0 8 | 2/3 | 0 4| 0 16
or f/8 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 8, | 1/20 | 1/6 | 1 | 1 20 | 1 20| 0 16 | 1-1/3| 0 8| 0 32
or f/11.314 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 16, | 1/10 | 1/3 | 2 | 2 40 | 2 40| 0 32 | 2-2/3| 0 16| 1 4
or f/16 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 32, | 1/5 | 2/3 | 4 | 5 20 | 5 20| 1 4 | 5-1/3| 0 32| 2 8
or f/22.627 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 64, | 2/5 | 1-1/3 | 8 |10 40 |10 40| 2 8 |10-1/2| 1 4| 4 15
or f/32 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 128, | 4/5 | 2-2/3 | 16 |21 0 |21 0| 4 15 | 21 | 2 8| 8 30
or f/45.255 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------
No. 256, |1-1/2 | 5-1/2 | 32 |42 0 |42 0| 8 30 | 42 | 4 15|17 0
or f/64 | | | | | | | | |
------------+------+-------+-----+------+-----+------+------+-----+------

The estimation of this correct exposure is probably the greatest
difficulty in photography, and it is particularly discouraging to find
plate after plate useless because the guess has been wide of the mark.
There are some here to-night who have spoiled so many plates that at last
they are prepared by experience for almost any contingency, and to those
I nave very little to say; but there are a