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BENJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



it to the covered ball. This acts as a syphon, and keeps the 

 ball moist. The graduated scale shows the degree of evapo- 

 ration. When this hygrometer stands at 15, the air feels 

 damp, from 30 to 40 we reckon it dry, from 50 to 60 

 very dry, and from 60 upwards we should call it intensely 

 dry. Price, $5.00. 



Conical Rain Gauge. (Fig. 622.) 

 The rain gauge is a simple cone 

 of copper, of a given shape and 

 capacity, which is placed in any 

 situation where it will receive its 

 due proportion of rain. It is usually 

 placed in a piece of wood, bevelled 

 out to fit the cone, and fastened to 

 a post about eight feet high ; the 

 cap is placed in the cone with its 

 base downward. However closely 

 it may fit, by being pressed into it, 

 there will still be sufficient room left 

 between it and the sides of the gauge 

 V IIBr to permit the water to pass to its 

 I bottom. Immediately after every 

 shower, or fall of rain, the water must be measured, and 

 the contents registered and then discharged. On this will 

 depend the accuracy of the account ; for, from the construc- 

 tion of the gauge, the degrees of the scale near its bottom 

 being the largest, small quantities may be measured with 

 greater accuracy by this than by the gauges commonly used. 

 The cap is intended to prevent evaporation before the 

 measurement is made, should that be accidentally delayed. 

 The measurement is made by putting down to the bottom of 

 the gauge, the point of the measuring stick, and applying 

 the distance between it and the water-mark to the scale. 



The graduation of the scale is by hundred ths of an inch 

 for the first three-tenths of an inch, and above that by 

 tenths and half-tenths. The intermediate distances may 

 be measured by the eye, and set down in decimals. When 

 showers or rains of short duration fall, it will be well to note 

 the A. M. and P. M., with the hours between the beginning 

 and end prefixed, in order that the time may be compared 

 with that of observations made at other places. If the rain 

 continues for any length of time, the observations should be 



