materially affect the accuracy of the instrument. The reasoning holds good for every latitude--degree of influence being the only difference. Having given the action of the earth’s form, mass, and rotation on the pendulum, there remain the disturbances due to expansion and contraction, owing to changes of temperature and those of atmospheric causes. The astronomical points to be observed are somewhat too fully laid down, but it must be remembered that an exact science requires the premises to be fully established before a sequence can be drawn. As the standard of time depends on the passage of a star or the sun, or any known celestial object, at a certain time across the meridian of the place where the observation is taken, it was absolutely necessary to give the modes of calculation, together with the disturbing causes. Moreover, a full appreciation of the indebtedness of horology to astronomy could not be obtained without a general knowledge of the change of the position of the major axis of the orbit described by the earth around the sun. Also, the difference between mean and apparent solar time was required to illustrate the use of the tables of equated time, the necessity of which will become patent when the use of the transit instrument for the establishment of time, or a fixed standard, is introduced. Also, the disturbing effects of the sun and moon collectively and relatively as to position, could not be passed, as they produce the precession of the equinoxes and the nutation of the pole--essential elements in the computation of time. Watch and Chronometer Jewelling. NUMBER ONE. This whole subject is well worthy an article both in a scientific and mechanical sense, whether we consider the delicacy of the operations or the intractable character of the material operated on--for there has been no improvement in the horological trade of more importance to accuracy and durability of time-keepers. The substitution of stone for common brass or gold bearings, was prompted by the inevitable wear of the holes from frequent cleaning, and the abrasion of the pivots, produced by the accumulation of dust with viscid oil; the pivot being cut away, or the hole opened too large. So long as the verge and cylinder were the prevailing escapements, the necessity for jewelling was not so strongly felt, except in the balance holes. The introduction of the lever escapement brought with it a better watch,--capable of more accurate time, but demanding an improved construction. An Italian, in 1723, first introduced the practice of using stone for bearings. He not only conceived the idea, but was successful as an artisan in making his own jewels; ingenious and skilful as he was, however, he encountered obstacles almost insurmountable.