Page:The museum, (Jackson, Marget Talbot, 1917).djvu/59

Rh can be taken care of. Such extreme measures, of course, call for more constant cleaning, but the safety of the objects and the comfort of the guards and visitors will be sufficient to offset this. A fine wire screen placed on the inside of these openings will keep out birds and insects. In winter, of course, these louvre vents can be replaced by solid doors which will keep out the cold.

Museums in the north must contend with winter snows. It is hard to keep skylights from leaking if snow is allowed to stay upon them, aside from the darkness of the galleries. Shovelling off the snow is a difficult process because of the danger of breaking glass. Steam pipes should be provided running just under the glass. When snow has fallen the steam should be turned on very slowly and the snow gradually melted away. Heat too rapidly applied will cause the glass to crack. A certain American museum has arranged a sprinkler system for use on the outer roof in case of excessive heat in summer. It has not been working long enough to permit a satisfactory judgment of its efficiency. The same system was tried in Nuremberg but failed because the water poured on the hot glass caused it to crack. A skillful and prodigal use of water might, however, prove effective.

For various types of skylight the reader is