In late 1928 Edwin Hubble was right in the middle of using VM Slipher’s 
redshift data to prove that the universe is expanding, when Hubble’s boss 
George Hale ordered him to drop everything and rush to the Grand Canyon 
to test it out as a site for his planned 200-inch telescope. (This Grand 
Canyon episode is a fascinating story in itself).  On his way, Hubble stopped 
at Lowell Observatory and visited with VM Slipher.  Both before and after this 
visit, Hubble wrote to Slipher, and Slipher wrote to others about this visit.  
There is no indication that Hubble ever said a word about his being in the middle 
of using Slipher’s research to transform the universe.  At the least, this silence 
was symbolic of the silence with which astronomical history would often treat 
VM Slipher and his work.