[13] The cost of the glass for one hive so as to give the air space all around, if purchased at the wholesale prices will not exceed 25 cts. Where three hives are made in one structure, the glass for the three will cost less than 50 cents; if double glass is not used, the expense would be less by one half.
[14] The observations to test the temperature of the Protector were made in Greenfield, Massachusetts, in latitude 42 deg. 36 min.
If a populous hive is examined on a warm Summer day, a considerable number of bees will be found standing on the alighting board, with their heads turned towards the entrance, the extremity of their bodies slightly elevated, and their wings in such rapid motion that they are almost as indistinct as the spokes of a wheel, in swift rotation on its axis. A brisk current of air may be felt proceeding from the hive, and if a small piece of down be suspended by a thread, it will be blown out from one part of the entrance, and drawn in at another. What are these bees expecting to accomplish, that they appear so deeply absorbed in their fanning occupation, while busy numbers are constantly crowding in and out of the hive? and what is the meaning of this double current of air? To Huber, we owe the first satisfactory explanation of these curious phenomena. These bees plying their rapid wings in such a singular attitude, are performing the important business of _ventilating_ the hive; and this double current is composed of pure air rushing in at one part, to supply the place of the foul air forced out at another. By a series of the most careful and beautiful experiments, Huber ascertained that the air of a crowded hive is almost, if not quite, as pure as the atmosphere by which it is surrounded. Now, as the entrance to such a hive, is often, (more especially in a state of nature,) very small, the interior air cannot be renewed without resort to some artificial means. If a lamp is put into a close vessel with only one small orifice, it will soon exhaust all the oxygen, and go out. If another small orifice is made, the same result will follow; but if by some device a current of air is drawn out from one, an equal current will force its way into the other, and the lamp will burn until the oil is exhausted.