Now as to distance, take the case of the second star. Subtract the first indirect reading from 100°, giving 0·5, and add this to the direct reading, 12·5, making 13·0, which is the difference between the two readings taken on either side of the fixed wire; the half of this, 6·5, is placed in the next column, and the same process is repeated with the next two readings: a mean of these is then taken, which is 6·6 for the number of divisions corresponding to the distance of the stars. In the micrometer used in this case, 5·3 divisions go to 1˝, so that 6·6 is divided by 5·3, giving 1˝·237 as the distance. A table showing the value in seconds of the divisions from one to twenty or more, saves much time in making distance calculations; the following is the commencement of a table of this kind where 5·3 divisions correspond to 1˝. ┌──────┬─────┬────┬────┬────┬────┬────┬────┬────┬────┬────┐ │Divi- │ 0 │ ·1 │ ·2 │ ·3 │ ·4 │ ·5 │ ·6 │ ·7 │ ·8 │ ·9 │ │sions │ │ │ │ │ │ │ │ │ │ │ │ of │ │ │ │ │ │ │ │ │ │ │ │micro-│ │ │ │ │ │ │ │ │ │ │ │meter.│ │ │ │ │ │ │ │ │ │ │ ├──────┼─────┼────┼────┼────┼────┼────┼────┼────┼────┼────┤ │ 0 │0·000│·018│·037│·056│·075│·093│·112│·131│·150│·168│ ├──────┼─────┼────┼────┼────┼────┼────┼────┼────┼────┼────┤ │ 1 │0·187│·205│·224│·243│·262│·280│·299│·318│·337│·356│ ├──────┼─────┼────┼────┼────┼────┼────┼────┼────┼────┼────┤ │ 2 │0·375│·393│·412│·431│·450│·468│·487│·506│·525│·543│ └──────┴─────┴────┴────┴────┴────┴────┴────┴────┴────┴────┘ In the first column are the divisions, and in the top horizontal line the parts of a division, and the number indicated by any two figures consulted is the corresponding number of seconds of arc. In the case of a half difference of 2·3 we look along the line commencing at 2 until we get under 3, when we get 0˝·431 as the seconds corresponding to 2·3 divisions.