. Discovery. Science. 1(10 I)IS(:ovi:hy Zainhra brought out a rcconliiig rain-(:;auge called the HydograpJi, constructed under Halliwells patent. This (k>ign was approved by Dr. Mill, and since then. FIG. 5.—THE " 1908 " (.Original Pattern). (1908) an improved form has been introduced, known as the " 1919 ; In Fig. 5 1 we see the original pattern instrument, and in Fig. 6 a sectional diagram of the 1919 improved apparatus. It should be mentioned that in Halliwell's Patent Rain-gauge the water in the float cylinder is made to siphon awaj^ To obtain
. Discovery. Science. 1(10 I)IS(:ovi:hy Zainhra brought out a rcconliiig rain-(:;auge called the HydograpJi, constructed under Halliwells patent. This (k>ign was approved by Dr. Mill, and since then. FIG. 5.—THE " 1908 " (.Original Pattern). (1908) an improved form has been introduced, known as the " 1919 ; In Fig. 5 1 we see the original pattern instrument, and in Fig. 6 a sectional diagram of the 1919 improved apparatus. It should be mentioned that in Halliwell's Patent Rain-gauge the water in the float cylinder is made to siphon awaj^ To obtain an absolutely trustworthy automatic siphon would be a great deal too expensive for use in a gauge at a relatively low price, and to obviate this difficulty the Hyetograph was constructed with a mechanical device which affects the pen only, and gives an open scale of ^ inch of rainfall recorded on a chart 3 inches high. When the Hj'etograph is in action, so long as rain is falling the float D (Fig. 7) continues to rise, up to a maximum capacity of j,\ inches. On a spindle E, rising from the float D, are a number of projecting pins FF which engage successively with a projection on the lever G, this lever being so piv^oted that when the pen reaches the top of the chart the lever dis- engages with the pin and falls by its own weight on to the next lower pin, which is so placed to allow the pm to fall to zero on the chart. The float therefore ' Illustrations reproduced by permission of Messrs. Negrctti nd Zambra. London. continually ascends during rainfall, but at each suc- cessive half-inch of rain the pen descends to zero and recommences its upward movement. As no automatic siphon is used, it is obvious that the rain will collect in the float-chamber until it is removed, and the float cylinder is made sufficiently large to allow an accumulation of over 4 inches of rainfall, the maximum usually likely to occur in one day in any locality in Great Britain and Ireland, except the w
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