this is easily effected with a low power; then the finder is to be fixed, by means of its wires, in such a position that the star shall be in the centre of the field of the finder when also in the centre of the telescope’s field.  When this has been done, the finder will greatly help the observations of the evening; since with high powers much time would be wasted in bringing an object into the field of view of the telescope without the aid of a finder.  Yet more time would be wasted in the case of an object not visible to the naked eye, but whose position with reference to several visible stars is known; since, while it is easy to bring the point required to the centre of the finder’s field, in which the guiding stars are visible, it is very difficult to direct the telescope’s tube on a point of this sort.  A card tube with wire fastenings, such as we have described, may appear a very insignificant contrivance to the regular observer, with his well-mounted equatorial and carefully-adjusted finder.  But to the first attempts of the amateur observer it affords no insignificant assistance, as I can aver from my own experience.  Without it—­a superior finder being wanting—­our “half-hours” would soon be wasted away in that most wearisome and annoying of all employments, trying to “pick up” celestial objects.

It behoves me at this point to speak of star-maps.  Such maps are of many different kinds.  There are the Observatory maps, in which the places of thousands of stars are recorded with an amazing accuracy.  Our beginner is not likely to make use of, or to want, such maps as these.  Then there are maps merely intended to give a good general idea of the appearance of the heavens at different hours and seasons.  Plate I. presents four maps of this sort; but a more complete series of eight maps has been published by Messrs. Walton and Maberly in an octavo work; and my own ‘Constellation-Seasons’ give, at the same price, twelve quarto maps (of four of which those in Plate I. are miniatures), showing the appearance of the sky at any hour from month to month, or on any night, at successive intervals of two hours.  But maps intermediate in character to these and to Observatory maps are required by the amateur observer.  Such are the Society’s six gnomonic maps, the set of six gnomonic maps in Johnstone’s ‘Atlas of Astronomy,’ and my own set of twelve gnomonic maps.  The Society’s maps are a remarkably good set, containing on the scale of a ten-inch globe all the stars in the Catalogue of the Astronomical Society (down to the fifth magnitude).  The distortion, however, is necessarily enormous when the celestial sphere is presented in only six gnomonic maps.  In my maps all the stars of the British Association Catalogue down to the fifth magnitude are included on the scale of a six-inch globe.  The distortion is scarcely a fourth of that in the Society’s maps.  The maps are so arranged that the relative positions of all the stars in each hemisphere can be readily gathered from a single view; and black duplicate-maps serve to show the appearance of the constellations.