344 Profs. Percy Frankland and Marshall Ward. 



One dish was filled to a depth of 3 in. with clear water ; one with 

 2| in. of CuSC^Am, and the other with 2^ in. K. bichromate. 



Under each of the two latter I placed a plane mirror, flat, on 

 which I laid the culture cell (quartz floor), and one of the "dummy 

 cells " with its black-bulb . thermometer. Under the water dish I 

 placed a culture a,nd its " dummy " control on a piece of slate ; and 

 by the side of this a culture and its dummy under a bell- jar darkened 

 with foil and brown paper. Under the bell-jar I also hung a ther- 

 mometer in the air. A.11 four pieces of apparatus were on a large 

 box outside the laboratory and looking east and north. 



The day opened with a clear blue sky and light wind, but a good 

 deal of white cloud (cumulus) came over after 10 A.M., and there was 

 some haze about I P.M. After 2 P.M. a magnificent clear blue sky. 

 The sun was on the box until noon, but it was often covered by white 

 clouds, especially from 11.45 to 12.15 or so. 



The following table (p. 345) gives the temperatures. 



The sowings were made in broth-gelatine drops about 10.30 A.M., 

 and were at once exposed as described. The dishes were so large that 

 no side light could get in, and I was certain that only the light from 

 the sky, after traversing the liquid, glass-bottom of dish, and thin 

 cover-slip, reached the drop. 



Bach dish had a thermometer in the liquid, and care was taken* to 

 avoid any complications arising from the cusp of light reflected from 

 the vertical walls. 



In order to meet the objection that the orange and blue liquids 

 and cultures varied so much in temperature during the first 1^ hours, 

 I made two new sowings at 2.30, and put one under the blue and the 

 other under the orange dish, exactly as before, and left them there 

 till 6 P.M., so that they got 3^ hours' exposure to the open sky only 

 no direct sun. The retardation in the blue is, nevertheless, nearly as 

 marked as in the other cultures. 



* After my attention was directed to the danger by noticing the high tempera- 

 ture to which the bichromate dummy cell was running at 11 A.M. ; only the dummy 

 was being touched by the cusp, however, so that the temperature recorded for the 

 actual culture cell at this moment is too high. 



