The proper temperature of the milk or cream is a point of great practical importance. If the fluid be too warm or too cold the buttery particles will only by great trouble be made to cohere; and the quality of the butter is almost certain to be inferior. When the whole milk is operated on, the temperature should be from 55 to 60 degs. of Fahrenheit's thermometer; and if cream be employed the temperature should never exceed 55 degs. nor be lower than 50 degs. Hence it follows that in summer the dairy should be kept cooler, and in winter warmer, than the atmosphere. The temperature of milk is raised or lowered as may be found necessary, by the addition of hot or cold water--in performing which operations properly, a good thermometer is indispensable; one should always be kept in the dairy, and should be so constructed as to admit of being plunged into the milk. In some dairies the water, instead of being mixed with the milk, is put into a tub in which the churn is placed. There is a good kind of churn, which consists of two cylinders, the one within the other--the interval between them being intended for the reception of hot or cold water. The influence of temperature upon the production of butter has been placed beyond all doubt by numerous carefully-conducted experiments. Mr. Horsfall, a celebrated dairy farmer, in discussing this question, sums up as follows:--"By a series of carefully-conducted experiments at varying temperatures, I am of opinion that a correct scale of the comparative yield of butter at different temperatures might be arrived at; as thus: From a very low degree of temperature little or no butter; from a temperature of about 38 degs., 16 oz. from 16 quarts of milk; ditto, 45 degs., 21 oz. from 16 quarts of milk; ditto, 55 degs., 26 to 27 oz. from 16 quarts of milk." This is a higher yield of butter than, I suspect, most dairymen get: but Mr. Horsfall's cows being of the best kind for milking, and well fed, the milk is, of course, rich in butter; and his experiments prove that even the richest milk will not throw up its butter unless at a certain temperature. In the churning of cream the motion should be slow at first until the cream is thoroughly broken up. In churning milk the agitation should neither be violent nor irregular; about 40 or 50 motions of the plunger or board per minute will be sufficient. In steam-worked churns the motion is often excessively rapid, and the separation of the butter is effected in a few minutes; but the article obtained in this hasty way very quickly becomes rancid, and must be disposed of at once. An hour's churning of sour cream appears in general to produce good butter. Sweet cream and whole milk require a longer period--the latter about 3 hours--but in any case prolonged churning is certain, by incorporating cheesy matter with the butter, to produce an inferior article.