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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



I assume that you do not think the radiation in free space would be as much 

 as 5 per cent the higher of the two. If so, the proposed balloon experiments 

 may be expected to be conclusive to you as well as to me, if you are satisfied 

 as to their accuracy. 



The apparatus is now in so forward a state of preparation that if you should 

 be in Washington I hope you will do me the kindness to come and see it and 

 discuss it. As that may be impracticable, I give the following details which 



