312 Forestry Quarterly. 



Hasluck, Book of Photography, 1905, p. 88, having been pre- 

 pared by Prof. A. Scott) shows the actinic (not thermal) ratios 

 for the various months and hours for latitude north 40". 



The present experiment was, however, started at about the 

 height of the shipping season, so that, from the standpoint of 

 present commercial practice, this variable may be ignored. 



The nursery is in about 41** 30' N. Lat., 15 miles from salt 

 water (New Haven Harbor), at an altitude of about 200 ft. 

 above mean sea level, on level ground. 



The sun's heat evidently varies in intensity from hour to 

 hour, and a series of hourly exposures might be made through 

 the day, but it was desired to try prolonged exposures as well, 

 and these, as, for instance, a lo-hour exposure, are evidently 

 rather limited as to time of day. A series of exposures varying 

 from one another in duration by ten minutes was, however, con- 

 ducted about noon. 



It is obvious that a cloudy day would be less harmful than 

 a brilliantly clear day. The day chosen happened to be clear 

 though not brilliant (see Table i), probably as nearly average a 

 day as obtainable. In the nursery practice much of the work 

 is done under shelter of some kind. Stringing the plants in the 

 transplanting boards is done under the shelter of burlap shanties 

 which give considerable protection from wind and perhaps half 

 protection from sun. Some of the counting and bundling is 

 done here, also. The greater part of this, however, as well as 

 all the packing, is done in the counting and packing sheds which 

 afiford complete sun protection and nearly complete wind pro- 

 tection, and it was only in the packing shed that the shade ex- 

 posures were made. 



The temperature, the humidity, and the precipitation do not 

 need comment, though perhaps the significance of the humidity 



