The development of dairying in the United States during the closing decades of the nineteenth century has been uninterrupted, and marked by events of the greatest consequence in the entire history. The importance of two inventions during this period cannot be overestimated. The first is the application of centrifugal force to the separation of cream from milk. This is based upon the specific gravity of the milk serum or skim milk, and of whatever impure matter may have entered the milk, such gravity being greater than that of the fatty portion or cream. The dairy centrifuge, or cream separator, enables the creaming or “skimming” to be done immediately after milking, preferably while the milk is still warm. The cream can be at once churned, while sweet; but a better practice is to cure or “ripen” it for churning: this can be done at a comparatively high temperature, dispensing with the necessity of so much ice or cold water. The skim milk is available for use while still warm, quite sweet, and in its best condition for feeding to young animals. This mechanical method is more efficient, securing more perfect cream separation than the old gravity system, and the dairy labor is very largely reduced. The handling and caring for the milk may be thus wholly removed from the duties of the household. A usual plan is to have a “skimming station,” to which the milk is hauled at least daily from the producing farms in the vicinity, and where one or more separators are operated by power. Separators are also made of sizes and patterns suited to farm use, where they may be operated by hand or by light power,—electricity, steam, water, a horse, a bull, a sheep, or a dog. Besides its economy and its effect upon labor, this machine almost eliminates the factor of climate in a large part of dairy management, and altogether has worked a revolution in the industry. The centrifugal separator is still a marvel to those who see it working for the first time: the whole milk, warm, flows into the centre of a strong steel bowl, held in an iron frame; the bowl revolves at a rate of 1500 to 25,000 times per minute, and from two projecting tubes cream and skim milk flow in continuous streams to separate receptacles. The machines can be regulated to produce cream of any desired thickness or quality. These separators, of different sizes, are capable of thus skimming or separating, or more properly, creaming, from 15 to 500 gallons of milk per hour. A machine of standard factory size has a speed of 6000 to 7000 revolutions a minute, and a capacity for separating 250 gallons of milk an hour. The world is indebted to Europe for this invention, at least as a dairy appliance. Yet investigations were in progress contemporaneously in this country along the same line, and many of the material improvements in the cream separator and several entirely new patterns have since been invented here. The first separators were put into practical use in this country