Above all, care must be taken to set down only what is seen with certainty, _and nothing more_. The drawing may be good or bad, but it must be true. A coarse or clumsy sketch which is truthful to the facts seen is worth fifty beautiful works of art where the artist has employed imagination or recollection to eke out the meagre results of observation. The astronomer's primary object is to record facts, not to make pictures. If he is skilful in recording what he sees, his sketch will be so much the more truthful; but the facts must come first. Such practical falsehoods as the insertion of uncertain details, or the practice of drawing upon one's recollection of the work of other observers, or of altering portions of a sketch which do not please the eye, are to be studiously avoided. The observer's record of what he has seen should be above suspicion. It may be imperfect; it should never be false. Such cautions may seem superfluous, but a small acquaintance with the subject of astronomical drawing will show that they are not. The want of a good lunar chart will speedily make itself felt. Fortunately in these days it can be easily supplied. The great photographic atlases now appearing are, of course, for the luxurious; and the elaborate maps of Beer and Mädler or Schmidt are equally out of the question for beginners. The smaller chart of the former observers is, however, inexpensive and good, though a little crowded. For a start there is still nothing much better than Webb's reduction of Beer and Mädler's large chart, published in 'Celestial Objects for Common Telescopes.' It can also be obtained separately; but requires to be backed before use. Mellor's chart is also useful, and is published in a handy form, mounted on mill-board. Those who wish charts between these and the more elaborate ones will find their wants met by such books as those of Neison or Elger. Neison's volume contains a chart in twenty-two sections on a scale of 2 feet to the moon's diameter. It includes a great amount of detail, and is accompanied by an elaborate description of all the features delineated. Its chief drawbacks are the fact that it was published thirty years ago, and that it is an extremely awkward and clumsy volume to handle, especially in the dim light of an observatory. Elger's volume is, perhaps, for English students, the handiest general guide to the moon. Its chart is on a scale of 18 inches to the moon's diameter, and is accompanied by a full description. With either this or Webb's chart, the beginner will find himself amply provided with material for many a long and delightful evenings work. [Illustration: PLATE XVIII. Chart of the Moon. Nasmyth and Carpenter.] [Illustration: PLATE XIX. Key to Chart of Moon. Nasmyth and Carpenter.]