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45
Three Leveling: Screws versus Four.
To the student of the progress in Engineers' field instruments, the question often
presents itself as to the comparative merits of an instrument provided with three,
over one having four leveling screws. It should be here remarked that the greater
portability existing in instruments provided with four leveling screws still commends
itself to all using the more customary class of instruments. However, the
finest class of field instruments, requiring spirit-levels corresponding to the fineness
of graduation, cannot be advantageously manipulated with tour leveling
screws. The results thus obtained would be little better than those obtained with
a more ordinary instrument. To insure the full benefit of a finer instrument, such
as used in triangulation, the maker will prudently apply three leveling screws,
mounted on a feasts larger then is usual in instruments with four screws. So, while
four leveling screws have the advantage of greater compactness and less weight
three screws have the advantage for closer setting, giving better results. The
maker will therefore adapt either the one or the other kind to his instruments aa
the c*se may require.
Quick Leveling Attachment.
[For illustration seepage 118.]
As all devices of this kind detract more or less from the stability of an instrument,
it seems they never have been regarded with much favor by the engineering
profession at large. There are cases, however, where the use of such a device, in
a mountainous country, or in underground work of a close character, becomes very
desirable. Messrs. C. L. Berger