I cannot think that any catalogue but the MS. one in zones (which was only intended for your own use) would facilitate the reviewing of the Nebulæ, and _you_ are the only one to whom 1885, viz., 2nd and 3rd class, out of the 2500, can be visible in your twenty-foot. Wollaston, who knew this, has given in his Catalogue only 1st and 4th, &c. classes of the first 1000, the second not having been published at that time, and they are without the yearly variation. Bode has given the first and second Catalogues complete, and calculated the yearly variation to each by de Lambre’s Tables. (See Bode’s preface, p. iv., line 18.) The last 500 were not published yet in 1800, or rather 1801. I only mention this that if you wanted the variations, and had a mind to trust to that catalogue of errors, it would save an immense trouble by copying them. But the more I think of these, the more I doubt if it would not be injuring the places of objects merely (though accurately) pointed out, to calculate them in the same manner as stars repeatedly observed in fixed instruments; and I doubt if your father noticed Bode’s having done so. You will find undoubtedly many more nebulæ which may have been overlooked for want of time, flying clouds, haziness, &c., especially in those sweeps which are registered _half sweep_. It is a pity time could not be found for making, as was often intended, a register in which the boundaries of the sweeps, with the nebulæ, were all brought to one time, either to Flamsteed’s or 1790 or 1800. The register in Flamsteed’s time, which is from 45° to 129°, is for that reason the best mem. At the time that register was made, the apparatus for sweeping in the zenith was not completed, and higher than 45° was not used. If you should wish in the latter part of the summers (when your father was generally from home) to fill up the unswept part of the heavens, you might perhaps discover as many objects as would produce a pretty numerous catalogue. You will see in the register of Flamsteed’s time a curved line which denotes that the Milky Way is in those places, and if you see an _L_ and find a cluster of stars thereabout, I shall claim it as one of those I mentioned in my last letter to you. It was the assistant’s business to give notice when such marks or any nebulæ in the lapping over of the sweep either above or below were within reach, by making the workman go a few turns higher or lower. (N.B. No more than is convenient without deranging the present sweep.) But I am forgetting myself, and fear I am tiring you unnecessarily, and will only add that if your father wanted at any time to review or to show any of his planetary or other remarkable nebulæ to his friends, the time and P.D. was, by the variation of its nearest star in Wollaston’s or Bode’s catalogue, brought to the intended time of observation, and P.D.—comp. of latitude, with allowance for refraction, gave the quadrant for setting the telescope.