1898 - 99 .] Dr Hepburn on Improved Form of Craniometer. 603 
skull, and as the results are obtained mechanically, the risk of error 
is largely obviated. 
Description of the Instrument . — The instrument presents various 
modifications of the craniometer in ordinary use (fig. 1). First, upon 
one side of the graduated bar, zero is placed at the centre, and the 
millimetre scale is duplicated from the centre towards opposite 
ends of the bar ; second, opposite zero, a straight calliper leg has 
been introduced. This leg is placed at right angles to the 
graduated bar, and being sunk in an undercut flat groove, it may 
be pushed backwards or forwards so as to alter its length relative 
to that of the curved legs of the callipers without disturbing its 
position at right angles to the graduated bar and without deflect- 
ing its pointed end from indicating zero on that bar. Further, a 
small flat spring sunk in the bar at the bottom of the groove 
assists in retaining this leg in any position to which it has been 
adjusted. Third, the two curved legs of the callipers are so dis- 
posed as to be both capable of gliding upon the graduated bar, and 
therefore since each of these legs may approach or recede from the 
central one, the edge of the armature which carries each curved 
leg indicates, upon the scale, the distance which the point of each 
curved leg is from the point of the central straight leg, i.e ., from 
zero. Fourth, the central leg may be removed (fig. 2), and the 
groove closed by a metal slip. Thereafter, since the reverse side of 
the bar is graduated continuously from one end, by fixing one of the 
curved legs by means of a screw, the instrument is converted into an 
ordinary craniometer (fig. 3) available for any of its usual purposes. 1 
It will readily be apparent that this three-legged callipers is 
mathematically correct in its mode of measurement, because since 
the curved legs of the instrument are of equal length, and as both 
of them are fixed at right angles to the graduated bar, the chord 
or diameter which they measure is an imaginary line parallel to 
that bar; and further, the central straight leg in its imaginary 
prolongation intersects the chord of the arc at right angles, and 
therefore segments the chord in the same proportions that it does 
the graduated bar. 
Through the very great kindness of Sir William Turner I have 
1 This instrument is made solely by Mr A. H. Baird, Scientific Instrument 
Maker, Lothian Street, Edinburgh. 
