

SUMMARY OF RESULTS AND SUGGESTIONS. 165 



i second. Prolonging the exposure to J or perhaps second, 

 gives a great increase in the area commanded ; and 1 second 

 may be taken as marking almost the limit of a really useful 

 exposure for the corona as a whole. If beyond this we wish 

 to secure the long rays, we must be prepared to expose for 

 100 seconds or upwards, sacrificing, of course, the inner corona 

 for this purpose. It is possible that we may find that ex- 

 posures of 200 or 300, or even longer, are advantageous. But 

 exposures of above 2 seconds until we get to 50 or 60 or 

 upwards require the most skilful manipulation in development 

 to render them of any service. Otherwise detail in the corona 

 proper is sacrificed without any sensible increase in the 

 representation of the streamers. 



One corollary of great importance for amateur photographers 

 results from these considerations. Where f/a is not greater 

 than 15, and the focal length is not greater than a feet, the 

 blurring in a stationary camera of a photograph exposed for 

 \ second is only T J 1F inch, which is practically imperceptible. 

 A sharp image of the whole of the main body of the corona, 

 inner and outer, can therefore be secured by a fixed camera, 

 and there is no need for equatorial or driving clock, heliostat 

 or ccelostat, with the consequent expense, weight, and trouble 

 of adjustment. 



The one and only caution to be borne in mind is that the 

 camera should be firmly and rigidly mounted. This deduction 

 from the results of the 1898 eclipse should lead to a large 

 number of cameras of considerable focal length being used in 

 the eclipse of 1900, resulting in an abundant harvest of fine 

 photographs on a sufficient scale. 



It would be well worth while to try and arrange for photo- 

 graphs to be taken on the Appalachian Mountains in the 

 United States, and in Algeria, with instruments of precisely 

 similar make and size. With an interval of 2 h 40 m in absolute 

 time between the exposures at the two stations, there would 

 be an opportunity for again examining, as in 1893. if the 

 corona showed change in a short interval of time, whilst 

 the photographs might possibly be combined in pairs in the 

 stereoscope. If this could be done successfully, our knowledge 

 of the true form and structure of the corona would be immensely 

 increased at a glance. 



E. WALTER MAUNDER. 



PHOTOGRAPHS OF THE PARTIAL PHASE.* 



IT would seem worth while to include amongst the subjects for 

 experiment during the next eclipse, photographs of the corona 



* By Mr. and Mrs. Walter Maunder. 



