It is scarcely necessary to observe to the reader, the propriety of all the glasses of the apparatus being perfectly clean before the observations; for if, after being laid aside some time, or by dust, &c. they should appear soiled, it will be necessary to wipe them previously with a piece of soft shammy leather usually sent in the box for that purpose, or a clean soft cloth. The two large lenses at F, Fig. 3, may be readily separated by turning aside the two brass screws that act upon a brass ring. From the various ingenious admirers of this sort of instrument, many improvements and alterations have been suggested; among several that have been communicated, those by the two following gentlemen appear to me the most deserving of notice, and which I shall leave to the reader’s judgment and experience. The Rev. John Prince, LL. D. now of Salem, Massachuset’s States, North America, a valuable correspondent and friend of our late author, transmitted to him an alteration in the construction; and of which I here insert the brief account, in nearly the words given by Mr. Adams. Dr. Prince applies a strong joint similar to that of a telescope at about the middle of the center part of the pyramidical box, and a sort of adjusting screw at the large end. The joint is nearly in the center of gravity, so that a very small motion is sufficient to bring any object less than an inch in diameter into the field of view. This motion is effected by two screws at right angles to each other; one screw raising or levelling the body, the other moving it sidewise, the screw at the same time forming a double joint to accommodate the parts to the movement.[31] [31] A figure of this, with an explanation, as recommended by Mr. John Hill, Wells, in Norfolk, may be seen in the Gentleman’s Magazine, Vol. LXVI. 2d part, page 897. In this particular, as well as in the deviation from the parallel position of the glasses to the surfaces of the objects, I think the construction not so simple and perfect, as that by rack-work and pinion applied by Mr. Jones. Probably, Dr. Prince had not, at the time of his contriving the joint-work to the box, seen or heard of the other method. His subsequent contrivances shew real ingenuity; and to the inquisitive in this instrument, will afford much useful entertainment and advantage. To secure the image formed upon the rough glass more completely from the light, at times essentially necessary, there is a pyramidical mahogany box, of the same size, to pack, when not used, in the body of the microscope; when in use, the broad end of this screen box is to be slid into the groove, from which the exterior cover at the end has been taken. This method is peculiarly useful in the day-time; as, by screening the large lenses from the light, it may even then be used with satisfaction.