184 PROCEEDINGS OF SECTION A. 
The apparatus I first devised and used was exceedingly simple 
in principle, and consisted essentially of a fine steel screw and 
wedge of glass, the incline of the latter bearing some definite 
ratio to the pitch of the former. This glass wedge travelled 
along a bed, or base-plate, also of glass, being kept in position 
by means of a slot cut along its surface. As the wedge was 
propelled forward by the screw it raised a vertical plate, 
accurately adjusted at right angles to the base-plate, and as 
free as possible from movement other than that imparted to it. 
by the wedge. To this vertical plate the slide, or disc to be 
ruled upon, was attached by means of a suitable cement. A 
platform, for the support of a sliding diamond carriage, bridged 
the base-plate and wedge at a suitable height, being, of course, 
arranged transversely to and in front of the vertical slide. 
With this roughly constructed apparatus I was able to pro- 
duce ruled bands, or groups of lines, ranging from 5000 up to 
50,000 lines per inch. The apparatus has since been com- 
pletely rebuilt, being variously modified and altered in accord- 
ance with experience gained, and the greater precision de- 
manded by the class of work subsequently undertaken. 
My work has tended mainly in the direction of perfecting 
rulings for micrometric measurements, and for test purposes. 
To accomplish this, I have had so to modify and improve the 
apparatus with which J first commenced work, as to render 
it capable of precise and accurate movements much less than 
.00001 in. Also to select and mount diamonds with knife 
edges of a fineness or keenness equal to the grouping together 
of lines less than .00001 in. apart, and yet of such strength and 
durability as to be capable of producing many thousands of 
such lines without material alteration in character. And, 
lastly, but by no means least, so to mount these rulings as to— 
exhibit them in the best possible manner, while at the same 
time ensuring their permanency as microscopical preparations. 
Dealing with these essential features in the order stated, I 
will first describe somewhat more fully some of the more im- 
portant modifications of the apparatus, the principal features 
of which are, as already indicated, a sliding table, carrying 
the plate to be ruled, elevated, or, more correctly, precisely 
advanced by a wedge propelled by means of a screw. Wedge, 
base-plate, screw, ruling table, and diamond carriage, are all 
supported by, or connected to, a single metal casting, resting 
upon and surrounded by a mahogany casing. Some parts are 
necessarily detachable ; for instance, the screw and its bear- 
ings, which is complete in itself, also the various sliding wedges, 
the pitches or gradients of which range from 1 in 2 to 1 in 100. 
These wedges, which are interchangeable, are all of glass, 
accurately ground, but not polished. Their contact points are 
