The toothed wheels give a slightly better efficiency, but the worm gear is somewhat smoother in its action and entirely silent; the noise of gearing can, however, be considerably reduced by careful machining of the teeth, as is now always done, and also by the use of pinions made of rawhide leather or other non-resonant material.
Anthracite coal in Pennsylvania is subjected to breaking between toothed rollers and an elaborate system of screening, before it is fit for sale.
In 1880 Marsh brought out Odontornithes, a monograph of the extinct toothed birds of North America.
The mandible is toothed but has no coronoid bone.
In rack railways a cog-wheel on the engine engages in a toothed rack which forms part of the permanent way.
The catkins of the poplars differ from those of the nearly allied willows in the presence of a rudimentary perianth, of obliquely cup-shaped form, within the toothed bracteal scales; the male flowers contain from eight to thirty stamens; the fertile bear a onecelled (nearly divided) ovary, surmounted by the deeply cleft stigmas; the two-valved capsule contains several seeds, each furnished with a long tuft of silky or cotton-like hairs.
The roundish leaves, toothed on the margin, are slightly downy when young, but afterwards smooth, dark green on the upper and greyish green on the lower surface; the long slender petioles, much flattened towards the outer end, allow of free lateral motion by the lightest breeze, giving the foliage its well-known tremulous character.
In the species on which the genus was founded the leaves, as the generic name implies, are cuneate and entire, or toothed on their anterior margina l in other cases they are deeply divided by dichotomy into narrow segments, or the whorl consists of a larger number (up to 30) of apparently simple, linear leaves, which may represent the segments of a smaller number.
If, for the single toothed wheel, be substituted a set of four with a common axis, in which the teeth are in the ratios 4: 5: 6: 8, and if the card be rapidly passed along their edges, we shall hear distinctly produced the fundamental chord C, E, G, C 1 and shall thus satisfy ourselves that the intervals C, E; C, G and C, C 1 are, 2 and 2 respectively.
The toothed wheel being set in motion, the edge of a card or of a funnel-shaped piece of common notepaper is held against the teeth, when a note will be heard arising from the rapidly succeeding displacements of the air in its vicinity.