270 KUNZ-STEBBINS— PHOTO-ELECTRIC PHOTOMETRY 



twin tubes were fastened on an equatorial mounting, but a driving 

 clock was unnecessary. (Note: the simple tubes were made of 

 four-inch down-spouts.) 



Slide 5. — The electrical connection from each cell was carried in 

 conduit to the galvanometer and battery inside the hut. Each cell 

 box could be detached from the mounting outside, and brought in 

 to the photometer bench. Here it was arranged that the cell could 

 be exposed to a standard amyl acetate candle at varying distances, 

 and also to standard low-voltage electric lamps. The same appa- 

 ratus was also used to compare the lamps with the full moon, and 

 thus to get an indirect measure of the corona in terms of moon light. 



Slide 6. — Two assistants operated the apparatus outside, while 

 the observers read the galvanometers. 



Slide 7. — Our expedition had the same unfortunate experience 

 with the weather that other parties had on the days preceding the 

 eclipse. The nights and early mornings were usually clear, but 

 clouds, increasing during the day, were usually worst about the hour 

 of the eclipse, 5 P.M. The picture shows the conditions thirty min- 

 utes before totality. 



Slide 8. — At six minutes before the critical time the sun was still 

 behind the cloud at the upper left-hand corner of the picture, but at 

 tw^o minutes before time the cloud had moved away, and during 

 totality the corona stood out in a perfectly clear sky. 



Results. 



We secured four complete measures of the light of the corona, 

 and of the sky background. When proper allowance is made for 

 the absorption of the earth's atmosphere, it is found that the total 

 light of the corona was 1.07 candle meters, just half the light of the 

 full moon. There has been a curious disagreement between observers 

 at previous eclipses, as values have been found ranging from one 

 fortieth to ten times the moon's light, a differejice of 400-fold. 

 These were results from photographs, but the more reliable determi- 

 nations seemed to indicate a value of one tenth full moon, five times 

 smaller than our value. The visual results are in much better agree- 

 ment, ranging from half up to one full moon, or from the same up 

 to twice our value. 



