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 dust and haze may extend this correction to more than one and one-half hours.

Measurement of Sunshine.—The adjustment for registration practised by the Weather Bureau is based on experience and is reasonable. The tube holding the thermometer should be inclined so that the recorder will register when the actual disk of the sun—not a shapeless blotch of light—can be discerned through the clouds of an overcast sky. It is better to make the adjustment when the sun is about two hours high, by inclining the tube. The observer must wait for such a day, and perhaps several trials may be necessary.

The computation of the total actual hours of sunshine may be made by any system which the observer finds convenient. If the total sunshine is not more than a few hours, it is perhaps most easily counted in the manner suggested in a previous paragraph—that is, measurement along the edge of a strip of paper. When the obscuration by cloudiness is slight, or is absent, the following method may be followed:

From the total possible hours for the day deduct:

The calculations may be made in detail on the back of the record sheet. On the face of the sheet these should be entered in the proper place:

By this, or by a similar method, the computation for the month is finished on the last day of the month. In Weather Bureau practise, minutes of time are reckoned in decimals of an hour, in the measurement of sunshine.

Sunshine records are approximate only; close calculation, however, will bring reasonably accurate results. At times