4li FOKKST DISTRIBUTION 



publication^, which show that the mean maximum at Helena, 

 Yellowstone Park and Kalispell were between (10 and S7 per cent 

 and that the lowest relative humidity of which there is a record 



' per .-nit at Helena in August. 



Table _ gives tin 1 mean daily relative humidity, maximum 

 and minimum for a period of three years and table 3 the mean 

 daily variations during the same period. The record was made 

 by a standard hygrograph under standard conditions and cor- 

 rections made from time to time by aid of a sling psychromcter. 

 The instrument shelter, on the University campus, was placed 

 in an area of natural prairie vegetation as dry as usually can 

 be found in the region. A mountain rising to the east shut off 

 the early morning sun, hut the station was fully exposed through- 

 out the rest of the day. 



From the table of mean daily variations it will be seen that 

 these may range from "><>', to 64%. The curve traced by the 

 recording pen shows, especially during the summer mouths, a 

 rythmic daily rise and fall, the maximum about (1:00 a. m.. the 

 minimum about 4:00 to 6:00 p. m. The pen in rising traces a. 

 more or less /ig/;ii- and irregular line until the maximum is 

 n-aelied. At this point there is usually a sharp peak, for the 

 maximum is of short duration, then a steady downward sweep 

 diirinir the day to the minimum late in the afternoon. The max- 

 imum of cadi day's record usually shows strong throughout 



T:iMe '2. Me-in daily relative humidity ai Miysoula. Max iiinm tnul 



minimum. 



.Me-iii dailv \ a ria t i<ui-< in Hie relative humidity ;it Missouhi. 

 .''I.. M.-li. Apr. May .him- July AUK. Sept. Oct. X.v. I ><. 



r,i r,i .- <;i c,7 !> r,:; w i^.s 



22 :> n r,M r,i .v_- .71 <;L' r,i r.i :u 18 



r.M7 -jr, L".I 88 n; i-j is .-,. r,i r,j r,r, 21 20 

 1918 





