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GENETICS: C. B. BRIDGES 
thus recorded on the plate. Their intensity indications at 40 spectrum posi- 
tions are reduced by aid of a special slide rule plotting machine. 
A pair of silver disk pyrheliometers is read simultaneously with each 
spectro-bolographic determination. Measurements of humidity, temperature, 
and barometric pressure accompany the bolometric observations. Also a 
pyranometer is employed to determine the total sky radiation. 
The young men find pleasant companions at the great copper mine at 
Chuquicamata. At present they are boarding with a Chilean family at 
Calama, but as both are good cooks they may wish to board themselves. The 
railway and the river both pass the town of Calama, so that there is no such 
desert isolation as might be feared. To the east are the Andes Mountains. 
The peaks in that neighborhood rise to 16,000 or 17,000 feet. Some are vol- 
canic but none of these are very near. 
We hope the work will be continued for several years at least, and that 
nearly daily observations may be obtained. The application of the results 
to meteorology is something which may prove to have great possibilities. 
To exploit them we must first possess a long and nearly unbroken series of 
solar radiation observations. 
MAROON— A RECURRENT MUTATION IN DROSOPHILA 1 
By Calvin B. Bridges 
Marine Biological Laboratory, Woods Hole 
Communicated August 23, 1918 
The recessive eye-color 'maroon' was one of the early mutations in Drosophila 
(found March 13, 1912). This eye-color was found in a stock culture of 
wild flies, and was at first supposed to be a new appearance of the recessive 
mutation 'purple' discovered about a month earlier. Genetic tests (crosses 
between the two lines, etc.) showed that the new color was not the old purple, 
but was a new mutation almost identical with purple in appearance but en- 
tirely independent in origin and inheritance. This was the first of our now 
numerous cases of eye-color 'mimics/ in which two distinct genes produce 
practically the same somatic effect. 
During the six months following the discovery of purple and maroon there 
were thirteen recorded appearances or 'purple' eye colors, which constituted 
our most striking 'mutating period' of 'epidemic of mutation.' Of these new 
'purples,' tests showed that the first, fifth, sixth, and thirteenth were maroon, 
while the rest were true purple. A study of the pedigrees showed that these 
maroons had come from two independent occurrences of the maroon mutation, 
while the true purples likewise came from at least two separate acts of muta- 
tion. Maroon has reappeared independently on two subsequent occasions, 
so that this particular mutative process has occurred at least four times. The 
