It is argued (and rightly so) by the advocates of iron wheels that case-hardened pinions should not be used, in consequence of their wearing with great unevenness, but such persons should be reminded that this objection is much greater in the instance of cast-iron wheels. A case came under my notice some time since of a clock made by a London house, with iron wheels, which after comparatively little time became entirely worn out and had to be removed, a result not at all surprising to those who are aware of the porous nature of iron. The TEETH OF WHEELS have to be made with the greatest skill and care in order that the entire mechanism shall work without friction, and shall not only temporarily keep time with regularity, but shall last for many years without renewal. Teeth should fit into one another without a squeezing pressure (which is equivalent to friction), but with exact uniformity of contact, the action being almost entirely between the teeth separating from each other and not between those which are approaching, i.e. in technical language, the action should be after the line of centres of the wheels and not before it. Church clocks were accustomed formerly to be made to go for thirty-four hours, and to be wound up every day; by the frequency of which winding the clock could be made to keep time with great accuracy, for regulating could be attended to as frequently, and no great variation could well occur in twenty-four hours. But the regulating, as a matter of course, requires a regulator, or standard, of time, which is not always to be found in country places, nor even is the man in charge of clock-winding always in possession of a watch sufficiently accurate to convey the time from the regulator if there were one to the Church clock. Of late, Church clocks are made to go eight days, and so the labour of frequent winding has been saved, while at the same time by extra care in the manufacture and fixing of a clock, there need be no necessity for frequently regulating it. PENDULUMS.