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 " HYETOGR.-VPH (.Original Pattern). 



(1908) an improved form has been introduced, known 

 as the " 1919 Hyetograph." 



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 wettest parts of the Lake District and on 

 high mountains. 



In order to remove the water the Hyetograph is 

 constructed with a specially designed hand-started 

 siphon which is actuated when desired ; this empties 

 the float-chamber of any water which may have 

 accumulated therein. 



The chart is wound round a cylinder which makes 

 one revolution in 24 hours ; the effective length is 

 10-8 inches, giving 0-45 inch for an hour. 



From this brief description of the instrument it 

 will be noticed that its advantage ov'er other apparatus 

 of its kind is its simplicity ; it has very few parts 

 to get out of order and it is very easj* to set up. A 

 good plan is to erect it over a 6-inch drain-pipe, the 

 large end of the pipe being uppermost, so that the 

 flange is level with the ground ; then when the water 

 is siphoned out of the Hyetograph it flows directly 

 into the pipe and so into the ground. 



The general principle of the 1919 Hyetograph is 

 similar to that already described, but has embodied 

 in it some important improvements. In the older 

 instrument the trace on the chart was a curve ; in 



the new one it is a straight line, and anyone who has 

 had experience in tabulating traces will at once appre- 

 ciate the advantage of this arrangement. 



