In order that some of the wonders of bee-work may be seen in the process of performance, various arrangements have been made, constituting what are called "Observatory Hives." In these glass is substituted for wood in the sides, shutters being fixed over them to exclude the light. In some cases Venetian blinds are used instead of shutters. The frames with the combs are sometimes arranged vertically in one or two series, and sometimes laterally a dozen or more standing one behind another. In the latter instance both the top and the sides are of glass. [Illustration: Fig. 58.--The Carr-stewarton Hive.] The whole hive may be made to revolve by means of two iron wheels, the one fixed to its bottom, the other to a stout board running its whole length. In the centre of the floor-board there is an opening into a passage below, which leads to the open air. This arrangement enables the hive to be turned in any direction without interfering with the egress and ingress of the bees. If the queen with her attendants cannot be found on one side of the combs, the other side may be brought into view by rotating the hive, and the different classes of the population can be studied, and their work surveyed in security and continuously. [Illustration: Fig. 59.--Unicomb Observatory Hive.] The unicomb hive may be stocked in various ways. The simplest plan is to take from a bar-frame hive the comb on which the queen is, and put it into the unicomb hive with as many more empty frames as will fill all the space intended for their reception. In this way new clean comb will be made, giving a much better appearance to the colony. Another plan is to take brood-comb in frames sufficient in number to fill the hive at once. The bees will then make a queen for themselves, and the interesting process may be watched in all its stages, provided, of course, that there are some freshly-laid worker-eggs in the cells. It is not advisable to try to keep the bees alive in an observatory hive during the winter, because so much heat is lost by absorption through the glass sides and top. It is best, therefore, to replace the frames and their tenants, early in the autumn, in the ordinary wooden hives.