148 
I)E. A. E. 11. TUTTON ON THE ELASMOMETEK, 
block. The azimuth adjustment is effected about a pivot o by two tangent screws I, 
directed horizontally towards each other and against a projection m, which they thus 
press lietween them, carried in a recess by the upper j^art of the block ; they work in 
a hearing-piece n fixed above the front end of the lower part. The adjustment for 
altitude is effected by means of three capstan screws, screwing through the basal 
llanges of the upper block, but not into the lower block, one on the right and two on 
the left side. After adjustment by these three screws and the two azimuth screws, 
the upper part of the block can be rigidly fixed to the lower part by means of a strong 
screw 0 (aiso acting as pivot) j^assing as a smooth shaft right through the upper part 
and screwing into tlie lower part; its square head is deej^ly countersunk in a well in 
tine top of the upper block, of adequate size to admit the end of a T-shaped capstan 
key, wherewith the screw is manipulated. The well is covered with a cap, consisting 
of a short tube fitting the well and furnished with a flat top, after removal of the key. 
The two upper parts of the blocks are 10 centims. long at the top, and they 
overhang the lower parts at the inner ends by about a couple of centimetres. At 
2 centims. below the top at the inner end in each case a recess is commenced, which 
proceeds horizontally for 2'5 centims., then downwards vertically for about 3 centims., 
and finally curves outwards again as a basal flange of 0’8 centim., corresponding to the 
side flanges. It is within the commodious space formed by these two recesses that the 
balance beam e with its pressure point d can be introduced, as also the apparatus pp'<l 
for supporting and adjusting the plate c of the substance under investigation. 
The platinum-iridium knife-edges ff are fitted in small dove-tail grooves in the 
under sides of the overhanging parts, as close to the ends as is compatible with 
rigidity. The platinum-iridium fittings are drawn out to a fine point at each end, 
the actual knife-edge being the truly straight line joining the two points. The latter 
project for 6 millims. on each side of the blocks, so that they are visible in the reading 
microscope when it is arranged over them. Each is labelled with an engraved letter, 
which is visible in the field of the measuring microscope simultaneousl}^ with the 
point. The left point of the back wedge is marked A and the right one B ; the left 
point of the front wedge carries the letter C and the right point is engraved with D. 
The lengths of the edges AB and CD have been made equal, and the azimuth 
adjustment enables AC and BD to be adjusted ec[ual. Two alternative j^airs of 
platinum-iridium wedges are provided. Those shown in position in fig. 3 are of 
isosceles triangular section, as offering the greatest rigidity of the knife-edge. They 
are preferable whenever the substance under investigation is of considerable hardness, 
and good-sized plates of it can be obtained. The alternative pair are shaped as 
shown at the foot of the main drawing ; f'f represents a section through them, and 
f" an elevation of one of them parallel to the edge and as seen from the other. The 
angle of the wedge is about the same as that of the fli’st paii‘, ljut is turned inwards, 
so as to bring tlie two sides nearly horizontal and veilical, vlth the apex (representing 
the knil'e-edge) the lowest point and also that nearest to tlie corresponding section 
