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 position on the roof must be determined by judgment and experience.

In open country and sparsely built localities, the shelter built after the plans recommended by the Weather Bureau should be used. This consists of a miniature house, 3 by 2 by 2 feet, with louvered sides and a removable top. The front may be let down when readings are made. The front should face the north. The shelter rests on braced legs which should be anchored firmly to the ground. The top of the shelter is likely to become hot enough to radiate heat to the thermometers. This may be prevented in part by a double roof with an air space, or by covering the roof loosely with asbestos cloth or with lino- leum. There can be no objection to placing the shelter in the shade of a tree that shields it from the afternoon sun, provided it is not less than 8 feet from trunk and branches.

In locating a place for a shelter it is a good plan to use a second thermometer in various positions, checking and comparing maxima and minima. Reflection and absorption