46 



NEBRASKA STATE HORTICULTURAL SOCIETY. 



the lower bulb more than that in the upper. Tliis causes the lower 

 air to exjiaiul and j)ush the mercury up until it comes in contact with 

 the wire C, which is soldered into the tube. The other wire, D, is im- 

 mersed in the mercury all the while, and as the two form an electric 

 circuit leading to the recording instrument, the rise of the mercury 

 to the wire C will close the circuit and register on the cylinder the fact 

 of sunshine; then when the sun goes under a cloud, the lower bulb 

 cools to the temperature of the upper, the mercury falls away from 

 the wire C, and so the circuit is broken and the sunshine record ceases 

 to be made on the cylinder. 



The result of observations on sunshine and cloudiness in eastern 

 Nebraska is shown on the chart. The broken line shows what per- 



centage of the time the sky is cloudy. It will be seen that the cloudi- 

 est month is May, when the sky is on the average 55 per cent over- 

 cast, or, what amounts to practically the same thing, there is sunshine 

 45 per cent of the day, while in September the cloudiness reaches its 

 lowest point for the year with an average of 41 per cent. 



The greatest amount of actual sunshine, however, in the different 

 months varies in a somewhat different manner. The longer duration 

 of daylight during the earlier months of summer more than compen- 

 sates for the lack of clear skies. The longest days of course occur in 

 June, when the average duration of daylight in this latitude is about 

 fifteen hours. This brings the season of greatest actual sunshine 

 earlier than it ap|)ears from the chart. In fact, the actual amount of 

 sunshine is greatest in the month of July, when it averages about 8.3. 

 hours a day; next in amount of sunshine comes August with an aver- 



