Remember That Story?

We all remember scenes or ideas from sf stories without necessarily remembering either titles or authors' names. Writing in 1945, CS Lewis acknowledged a story in an American "Scientifiction" magazine. That long ago, the story cannot have been written by Poul Anderson. When the story's protagonist had travelled into the past, raindrops pierced him like bullets and his teeth could not penetrate a sandwich:

"...because, of course, nothing in the past can be altered."

-CS Lewis, The Great Divorce (London, 1946), p. 9.

Anderson fans think, "No need for a Time Patrol then!" But there is more to it than that, isn't there? Presumably, this time traveller would not be able to move because air molecules would not get out of his way? The author imagines that past events retain their unalterability even when the traveller has arrived among them, when he has made them his present, as they say in Anderson's Time Patrol series.

No one else has written a story about a pastward time traveller pierced by raindrops or unable to move objects. If he is unable to alter events, then this must be for some other reason as ingeniously investigated by Anderson in works that do not involve the Time Patrol or by Audrey Niffenegger and some others.