MEASURING FROST

King Country Chronicle, Volume XXX, Issue 4860, 18 June 1936, Page 7

MEASURING FROST

EXTREME CARE NECESSARY. The difference in thermometer readings as illustrated in the published recordings of the number of degrees of frost in various centres, was discussed with a representative of a contemporary by one who has acted as climatological officer for the Government for the past 16 years. Apart from variations in frost currents, which naturally affected the temperature in various localities, the speaker remarked that it was very easy for an inexperienced person to make an error. Even the lifting of the thermometer quickly might affect the reading by a degree or two. Sometimes a thermometer filled with mercury was used, but these were by no means as accurate as those containing spirit. In placing the instrument in position on two forked sticks, care had to be taken that the bulb was clear of the grass. The instrument should be two inches clear of the grass. It had been proved that damp would affect a reading by as much as seven or eight degrees, so it could be seen that, a blade of grass touching the bulb would give a false reading.

A thermometer filled with mercury might register as much as three degrees lower than a spirit filled instrument. A sudden jerk in lifting the suspended thermometer might easily alter the reading one or two degrees, so that it could be seen that extreme care had to be taken all round. It was his custom to carefully mark the degrees of frost before lifting the instrument. Another factor which might account for variations was that it had grees of frost were registered. His own readings for his district were always taken from freezing point on the Fahrenheit thermometer, which was 32 degrees. Dr Kidston, how ever, had recommended that the cal culation be made from 30.4 degrees.

The layman was often well out in his estimate of the number of degrees of a frost, mostly because lie did not know the number of hours it had been freezing. A steady frost of seven or eight degrees all night would present far more evidence than a frost of 12 or 13 degrees which only came in the very early hours of the morning.