Licence: Public Domain Mark
Credit: On a universal indicator for microscopes. Source: Wellcome Collection.
Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.
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![through the same numbers on two vertical axes of the Indicator as remote from each other as possible. In some positions of the slide the axes A, and B' can be used for this purpose; in others A, and A', or B, and B' must be employed. The horizontal line of the slide being arranged as just directed it will be found that at least one of the vertical guide lines of the slide will intersect the horizontal graduation. By observing now the numbers at which the guide lines respectively stand, the record can be made. Suppose for example that the horizontal guide line ruled upon the slide intersects the verticals of the In- dicator at 43, while the right hand vertical of the slide cuts the horizontal series of numbers of the Indicator at 75; the entry to be made for this object in the register would be written thus and whenever that particular object is to be found either by the same Indicator or any other copy of it., if the slide is placed at these numbers and the Indicator is properly centred, the object must be in the field of view. In the same manner any number of objects can be registered or found. If the slide happens to be so placed that both of its verticals intersect the graduated portions of the horizontal line C, D, the position of either one of them can be recorded at will. If a guide line upon the slide falls between two divisions of either scale, the fraction of the division may be estimated with sufficient accuracy by the eye or a hand magnifier and entered in the register. Thus the recorded position would mean that the vertical lines of the Indicator were intersected at ]th of a division of the scale beyond 25, while the vertical guide line of the slide passed ^th of a division beyond the number 34 of the horizontal scale, as nearly as could be estimated. It is convenient to let the lower edge of the glass slide rest against a straight edged guide piece which can be moved parallel to the horizontal line of the Indicator. By pushing the slide along this edge, all the objects on the same horizontal can be found without changing the position of the guide piece. By moving the guide piece a little forward or back another sweep across the slide may be made, and so on until every object of interest is found. By following the directions above given it will be found that the recording or finding of objects by means of the Indicator is very easily performed, and scarcely requires the time which has been employed in describing the method. It is believed that the explanation above given is sufficiently explicit to enable any one to use the Indicator; but some additional remarks will now be .made upon the reasons for adopting the particular arrangement I have used, the modes of insuring accuracy in manipulation, and the modifications of which the Indicator is susceptible for'indi- vidual convenience.](https://iiif.wellcomecollection.org/image/b22274091_0005.jp2/full/800%2C/0/default.jpg)
