166 CAPTAIN A. E. CLARKE ON THE COMPARISON OE ENGLISH AND EOREIGN 
Suppose now we have two bars lying alongside one another in a box (the boxes are of 
a uniform breadth of 8 inches externally), their axes parallel, and about, as usual, 
3 inches apart ; then by the movement of the upper carriages, the one bar and the other 
may be brought alternately under the microscopes. 
Bars . — The various copies of the standard yard are all 1 inch square in section, and 
about 38 inches in length. At about an inch from either extremity of the bar, a cylin- 
drical well is drilled halfway through the metal; at the bottom of each w r ell is a gold 
pin let into the bar. On the surfaces of these gold pins, which are, it will be observed, 
in the neutral axis of the bar, the lines defining the measure are drawn. The bar has 
also wells in its upper surface for the bulbs of two or four thermometers. That particular 
copy of the standard yard which has been compared with all the geodetical standards 
is No. 55 (Swedish Iron) ; it is supported on rollers at one-fourth and three-fourths of 
its length. 
Ordnance Survey Standard Q r — This is a bar of wrought iron 10 feet 2 inches in 
length, 1-| inch broad, and 2\ inches deep ; supported on rollers at one-fourth and three- 
rfourths of its length. The ends of the bar are cut away to half its depth, so that the 
dots marking the measure of 10 feet are in the neutral axis of the bar. There are two 
wells for thermometers. 
Ordnance Intermediate Bar OI 1 is of wrought iron, in section having the form of a 
girder, with equal upper and lower flanges, the extreme breadth and depth being the 
same as in the last-mentioned bar. On the upper surface are seven disks, a, b , c, d, e,f, g : 
the spaces a b and fg are each one yard ; b c, c d, d e, ef are each one foot. Each disk 
has one transverse, crossed by two parallel longitudinal lines. This bar is supported on 
a cradle system of eight rollers. 
Indian Standards I s , X B are bars similar to one another and to the bar 01 described 
above, differing only in this, that one is of cast steel, and the other of Baily’s metal or 
bronze. 
Ordnance Toise (T 0 ) and Metre (M 0 ). — These bars are of cast steel, similar in section 
to the last-mentioned bars, but only an inch wide by one and a half deep. The toise 
has four disks, a, b, c, d; the spaces a b, b c are each one yard ; cd is approximately 4 - 74 
inches. It is supported on a cradle system of eight rollers. The metre has three disks ; 
the first two are a yard apart, the second and third are 3‘37 inches apart. 
Prussian and B.elgian Toises T 10 , T u are fiat bars of cast steel, an inch and three- 
quarters in breadth and four- tenths of an inch thick, terminating in cylinders about half 
an inch in length, the axis of the cylinder coinciding with that of the bar, and the dia- 
meter of the cylinder coinciding with the depth of the bar. At the extremity of each 
of these cylinders is affixed a smaller (co-axial) cylinder of tempered steel, an eighth of 
an inch in diameter, and only a sixtieth of an inch long. The faces of these small 
cylinders, Avhich are perfect planes beautifully polished, and at right angles to the axis 
of the bar, form the terminal planes of the measure. 
Bussian Double Toise P is also an end measure, but the terminal surfaces are nor 
