How often the repairer--clean he his work as well as he may--replace he the broken or worn part to put the time piece in as good condition as new--finds that its rate changes, that is loses time before long, and, at the end of one year is badly out of repair, solely the result of lack of knowledge, or negligence, in properly lubricating, or on account of an oil having been used which was not suitable. The object of this paper is to present in concise form the best of that which is furnished by the literature of the profession, together with that which has been written on friction and lubrication in general (so far as it may be applicable), by those not connected with this particular vocation; as well as the result of the practical experience of the manufacturers of time pieces in this country most of whom have furnished much useful data in answer to queries on the subject. The manufacturers of oils have also assisted by contributing valuable information. The result of the author's experience, observation and experiments will also be incorporated; and he will be grateful to any who may read this work, who will call attention, through the trade papers, to any errors of omission or commission that they may find therein. CHAPTER I. LUBRICANTS IN HOROLOGY--THEIR SOURCE AND METHOD OF REFINEMENT. ~1. As but little~ is to be found on the subject in the literature accessible to most of the craft, a few remarks concerning the source and general methods of refining the oils used in horology will, no doubt, be of interest. A mechanic who would work intelligently should possess a thorough knowledge of the materials constantly used, and oil is used on every horological mechanism. In order that this paper may be of maximum benefit and interest, the author has spared no pains in procuring useful data. ~2. Porpoise Jaw Oil and Black Fish Melon Oil~ (64) have become widely known and justly celebrated in all parts of the world, as they were found to be better adapted for the purpose of lubricating fine and delicate machinery than any substance _previously_ used. ~3. Blackfish-Melon Oil~[1] "derives its name from the mass taken from the top of the head of the animal reaching from the spout hole to the end of the nose, and from the top of the head down to the upper jaw, from which it is extracted. When taken off in one piece this mass represents a half watermelon, weighing about twenty-five pounds ordinarily. When the knife is put into the center of this melon the oil runs out more freely than the water does from a very nice watermelon. Porpoise jaw oil and blackfish melon oil are worth from $5 to $15 per gallon, according to supply. They are not only used in horology, but by manufacturers of fine firearms, philosophical apparatus, and in government lighthouses for the clocks of revolving lights."