Page:Handbook of Meteorology.djvu/224

 The ink used consists usually of glycerine, water and color pigment. If a permanent record is required black ink is preferable; green or blue is fairly permanent; red and purple fade in the course of a few years. A red ink with a madder or a genuine carmine base will not fade. Aniline red inks are marketed as “carmine,” however, and they are not at all permanent.

The pen of the barograph has a sleeve which slips over the end of the pen arm. It is not always easy to remove it when the pen requires cleaning. If it cannot be removed from the pen arm, lift the drum off the spindle; hold the pen firmly and clean with a small camel’s hair brush and water. Before filling the pen, draw a narrow strip of paper or a very thin spatula blade through the prongs of the pen in order that the ink may flow freely. With reasonable care for its cleanliness the pen will make a sharply-cut line; a foul pen leaves its own record.

The milled screw in the bar directly over the vacuum chamber adjusts the pen so that it has the correct position on the record sheet. The pen may be adjusted to record sea level pressure; but, as a rule, it is better to keep local pressure. The record sheets are usually lithographed with figures ranging from 28 to 31 inches. They are lithographed for other altitudes and also without any altitude marks. A “long-range” barograph, registering from 25 to 31 inches, is also made. Metric charts may be obtained from dealers in meteorological supplies.

When a barograph is to be moved—if carried otherwise than by hand—the drum and the ink bottle should be removed and packed separately. The pen arm should be fastened loosely to the switch rod. A dozen thicknesses of tissue paper or of soft cloth should be wrapped around the glass case and stand; they should be fastened so firmly that the parts cannot jostle. With an additional protective wrapping of heavy paper the instrument will ride safely in the packing case. There should be no packing of any sort around the vacuum chambers and levers.

If the barograph is carried by hand, the drum need not be removed from the spindle, but the pen arm should be thrown from the drum. A handle should be fixed to the package so that it may be carried in its proper position.