With a small portrait lens (the most useful size is about six inches) essentially everything about a comet will be shown as quickly as with a larger one. The main advantage of the large lens would lie in its greater scale—which of itself is of great importance. Another source of danger is moonlight, especially in the case of a long exposure. Nevertheless, according to Professor Barnard, important results may be obtained in full moonlight, if the comet is not too near the moon. Much, however, will depend upon the clearness of the atmosphere; the purer it is the less will the moonlight affect the plate. In this case a dew-cap helps much. On an ordinary moonlit sky an exposure of half an hour with a quick portrait lens will not ruin a fast plate if the comet is not too near the moon. In full moonlight, however, a longer exposure, unless under exceptional conditions, will seriously injure or ruin the plate. With the half-hour exposure the plate will be fogged, and of course the best quality of negatives cannot be obtained therefrom. All plates should be backed to prevent halation. A backing made of sugar and burnt sienna is recommended as entirely satisfactory, and can be kept in stock. The formula as supplied by the Cramer Dry Plate Company is as follows: Cook two pounds of granulated sugar in a saucepan, without the addition of any water, until it is nearly in the caramel or fudge stage. Then stir in one pound of burnt sienna and cook a little longer, stirring well. Do not let the backing get sticky, or it will be difficult to handle and will not soften so readily when removed from the plate. Finally add about half an ounce of alcohol to each pint as a drier. Put away in a wide-mouthed stoppered bottle or jar. When needed for use, dilute a little of this with water to the consistency of a thick but not too wet paste. Apply (not wet enough to run) to the back of the plate with a wide camel’s hair brush. It is not necessary to back heavily. A sheet of soft paper (an old newspaper) pressed on the backed surface will prevent injury to the plate, which should be freshly backed when ready for use. If kept in stock a long time after being backed, an unequal fogging is likely to occur. Before developing, remove the backing while it is still damp, with a moist piece of absorbent cotton. Should a small amount remain it will not affect the developer seriously. The plates should be carefully dusted with a broad soft camel’s hair brush, after being put in the plate-holder. The camera tube should be wiped out frequently with a damp cloth to free it from dust. It should also have a tight-fitting cover at the plate end to keep it closed when the plate-holder is not in position. There should be four springs, one at each corner, on the back of the plate-holders, to press the plate forward in a constant position.