FROST— OBSERVATIONS OF THE ECLIPSE. 285 



Vol. 40, pp. 241-258, 1914). While this method would be quite dif- 

 ficult of application and there might be a reasonable doubt as to 

 whether sufficient exposure could be given to secure a proper im- 

 pression of the rings from the green coronal line, nevertheless a suc- 

 cessful photograph would be of the greatest value, both for studying 

 internal motions of the corona and its rotation as a whole. 



I had the great advantage of discussing this with M. Fabry 

 during his visit to the United States as chairman of the French Sci- 

 entific Mission. He very kindly offered the loan of the apparatus 

 used at Marseilles, and, if it had arrived in time, we should have 

 tried the method, employing a rather small image of the sun in the 

 hope of getting sufficient intensity. Unfortunately the apparatus 

 did not reach us until long after the eclipse. 



I hope that this method will be properly tested at some future 

 eclipse. 



The flash spectrum as hitherto photographed has represented a 

 composite of the successive images of the dift'erent reversing lines 

 during the critical second or two at second and third contacts. Ex- 

 ceptions to this have been the instances where Professor Campbell 

 has employed a falling plate. I am not sufficiently familiar with 

 the results thus obtained, of which I have not seen reproductions, 

 to know how definitely the different stages of the brief phenomenon 

 are recorded. It seemed to me that the movie camera was at pres- 

 ent in a sufficient state of development to be successfully applied to 

 this problem. A " Universal " type of camera was employed, with 

 its short-focus lens removed, and this was attached, without altera- 

 tion or injury to the machine, to an objective-prism spectroscope 

 having three large Mantois prisms and a special camera lens of 5 

 cm. aperture and 40 cm. focus. This gave a scale of 13 A per mm. 

 in the vicinity of Hy. Only a small portion of the spectrum can 

 be photographed with the commercial machine because of the size 

 of the film, which allows an image i inch X ^ inch (25 mm. X 18 

 mm.). A region would naturally be selected in which important 

 lines occurred, or such as it was desired to study particularly. The 

 correct exposure was naturally a question of some uncertainty in 

 advance of the event. This is, of course, determined by the rate at 

 which the crank of the machine is turned. It is arranged for eight 



