REACTIONS TO LIGHT AND GRAVITY IN DROSOPHILA 91 
wave lengths transmitted by each, were as follows (table 22). 
The spectrum tests were made often enough to make sure that 
no fading of the colors was taking place. 
TABLE 22 
FORMULA WAVE LENGTHS 
\VVEHIGITC: conn oupennctewnl) Ge. 5380 A° (green)—4240 A° (violet 
Violet (Ammonia ton mace Green strong at 4950 A° 
Eee Copper sulphate Violet strong at 4510 A° 
(tiliten) heererrrce 7.5 grams | Blue, weak 
Wiaiheritncs tyakicy SUOROMCcE 5660 A°-5050 A° 
Gr Licht griin........ 0.03 grams | Strongest at 5320 A°® 
goer ts Napthol yellow... 0.25 grams 
Napthol green.... 0.03 gram 
Red WENGE codecsness a0) CoE 7200 A°-6325 A° 
Paeei eee Ponceau Red..... 3.0 grams | Strongest at 6570 A° 
The above formulae were only selected after a long series of 
experiments, and are for the most part modifications of formulae 
contained in the ‘Methods of Studying Vision in Animals” by 
R. M. Yerkes and John B. Watson, Behavior Monographs, 
1911. The red and the green are very satisfactory for colors 
obtained by ray filters, while the so-called violet is evidently 
not so good. It is, as a matter of fact, continuous from green to 
violet. The blue, however, is very weak, the green moderate 
and the violet band very strong and wide. The results of the 
experiments show that it is probably not the green to which the 
effectiveness of this filter is due, and since the blue band is so 
slight, the probabilities are that violet is the effective stimulus. 
It is practically impossible to get a strictly violet filter. We 
find, however, that blue is obtainable, and it is intended to use 
such a filter in analyzing our results further at the earliest 
opportunity. 
Besides the wave lengths, the relative energy transmitted by 
the filters was also measured by means of a thermocouple, using 
the same source of light employed during the experiments. The 
results are indicated in graph 4. From this it appears that if the 
energy transmitted by the colorless flasks be represented by 100 
