THE RELATION OF METEOROLOGY TO HORTICULTURE. 



15 



Meteorology is less concerned with the part which water plays in the 

 phenomena of plant and animal life than with questions concerning its 

 supply and the amount of rain which may be expected to fall, under 

 average conditions, in a particular district or country : the question 

 of the adequacy of the supply to the requirements of any particular 

 species or phase of plant life belongs to the domain of the horticultural 

 physicist. 



To obtain the required data for answering questions respecting this 

 important factor of the climate of any region the meteorologist regularly 

 measures the fall of rain, in order to find the average fall and also its 

 distribution as regards time. His measurements are made by means of a 

 rain gauge, which is a very simple instrument, consisting of a cylindrical 

 vessel, generally either 8 inches or 5 inches in diameter, which is placed in 

 the ground at an exposed spot, with its rim 1 foot above the ground 

 level. The water which falls into it is measured in a graduated glass 

 vessel of much smaller diameter, so that a fall of rain which, spread 

 over the area of the gauge, would measure, say, but a tenth of an inch 

 would fill the glass to the depth of perhaps an inch, and thus make it 

 possible to read with accuracy falls of rain which, spread over the surface 

 of the ground, would not be more than a hundredth of an inch deep. 

 Such a gauge is read daily, and usually at 9 o'clock each morning. 



There are several patterns of rain gauge in use, but all of them do 

 not fulfil the requirements of a reliable instrument. The aperture of 

 the gauge should, of course, be true in shape, and it should have a sharp 

 rim, so as to prevent splashing of rain- drops falling upon it. Besides 

 this the aperture should be sufficiently deep to prevent rain from 

 splashing out, or snow from being blown out, when once it has fallen 

 into the gauge ; and finally the receptacle for the water should be 

 protected against loss by evaporation by the gauge being sunk to a fair 

 depth in the ground, and by causing the water to pass into the receiver 

 through a small aperture and pipe, with which the inverted cone-shaped 

 opening of the gauge terminates. 



It is, however, for many purposes desirable to know something of the 

 rate at which rain falls, and frequently it becomes important to know 

 the precise time at which a fall of rain occurred, or the distribution of 

 the fall over the day. 



For these purposes a self-recording gauge is used, in which the rain 

 as it falls is made to actuate a pen, which marks the rate of fall by a 

 line traced upon a piece of paper, the paper being made to turn at a 

 uniform rate by means of a clock. 



There are several forms of recording gauge in use. In some the 

 rain passes into a balanced bucket, which, when filled to a certain point, 

 tips over and empties itself at the same time that it moves the pen by 

 turning a toothed wheel one notch ; simultaneously another bucket is 

 brought up on the opposite side to be filled, the two buckets thus 

 alternating in a kind of see-saw movement. 



In another gauge, known as Beckley's gauge, the rain passes into a 

 receiver which floats in a vessel filled with mercury. As the receiver fills 

 it sinks, and carries down with it a pen attached to it by a strip of 

 metal, which, as before, makes a mark upon a clock-turned strip of paper. 



