1870.] DOUGLAS — ON OBSERVATIONS OF TflE SUN. 133 



in the eastern limb, which, throwing out long tongues of light, 

 have the appearance of delicate flickering flames, in many cases 

 disconnected from the surface of the sun. In the second picture 

 the chromosphere is visible only on the western limb., and is less 

 brilliant than that on the eastern. 



J3y the three parties under Prof. Morton thirteen pictures in 

 all were taken during totality, with exposures varying from 5 to 16 

 seconds, all more or less successful. All display the chromosphere 

 and protuberances, and one of them, taken the instant before 

 totality, shows the limb of the sun cut into bright dots by the 

 mountainous ed";e of the moon, settliua', Professor Morton thinks, 

 conclusively, the question of the origin of Bailey's beads. The 

 exposure in all cases was too short to secure the corona ; but this 

 was most admirably done by ]Mr. Whipple at Selbyville, who 

 exposed a plate in the principal focus for 40 seconds. Even in 

 this picture the chromosphere may be detected as a very bright 

 ring within the crown of light, but all detail is smothered ; for, so 

 actinic is the light issuing from the chromosphere, that probably 

 no picture was exposed briefly enough to catch all the detail in its 

 structure and that of the protuberances, which the photographic 

 plate is capable of delineating. If any attempts are made to 

 photograph the eclipse which will occur in China this year, the 

 aim sliould be by very short exposure — say one second in the 

 principal focus — to secure the utmost possible definition in the 

 chromosphere. As these protuberances are ever in motion, reha- 

 ble deductions as to their structure can be drawn only from 

 pictures taken with a very short exposure. From the rapidity 

 which my plates — exposed only ten seconds — developed, I am 

 satisfied a well-defined image of a protuberance can be taken in 

 one or two seconds. kSo short an exposure would only give the 

 larger masses of the chromosphere, whose light, from the great 

 accumulation of light-giving material burning in them, is very 

 strong; but it should suffice for giving the most minute detail in 

 these masses — detail which is obliterated or blurred in pictures 

 with a longer exposure. 



During totality we took four pictures, of one inch diameter, in 

 the principal focus of the large telescope of the Quebec Observa- 

 tory, which Capt. Ashe had the courage to take with him, and 

 the skill to pack, mount, and re-pack without accident. Our 

 instrument was a nine-foot equatorial, made by Alvan Clarke, of 

 Cambridge, Mass. Our pictures received an exposure of ten 



