P. Schuyler Miller was one of the earlier SF writers, and this is one of his later works, written in 1944. He is noted, but not too notable.
This is a time travel story of some sort.
Interesting start. Once again we see an example of how much difference computers have made to the craft of analysis. The protagonist in the opening scene is pouring over charts and graphs he is making and describing the kind of secondary analysis he is having to do personally to create these charts.
This is taking place in a near future. Miller introduces concepts of personality customization in this near future but not computerized data crunching. But he is describing a technology revolution. He's talking about before-and-after of an invention that revolutionizes archeology.
Good! He puts some detail into the crafting of the time machine and he also describes setbacks in the researching to make it happen. There's a lot of craftsmanship described and not much science theory or computation. Once again, the lack of computer intrusion is glaring.
Miller describes the problem of a universe forking into two if a person travels back in time. He declares this doesn't happen when traveling into the future because the travel is in that case preordained. By the late forties time travel paradoxes had been well explored by SF writers.
He does a nice job of describing "personal effort" science research. This is the opposite end of the Manhattan Project-style science where thousands must be coordinated towards a single goal. It's a lot more interesting to describe, and read about.
This may be a one-man project, but it's not a small one! He describes having massive power lines installed directly from a power plant, and constructing a big concrete base in his laboratory in the back of his house for the machine. (I wonder what zoning commission let that happen! LoL!)
Nice description of the ancient knife, and a nice description of Walter Toynbee bringing it back and then dieing just a bit mysteriously shortly after the time travel. And nice description of his son husbanding the family rescources. Miller is old enough at this time to be sensitive to these practical issues.
The knife is a classic SF McGuffin -- some material unknown to modern science -- but Miller handles arriving at this conclusion well. It takes three full paragraphs. It's not some scientist taking a quick look, having an examining tool bounce off, and simply exclaiming, "This is nothing like we've ever seen before!"
What follows is a nice description of science people trying to deal with this mystery. It's good Technofiction.
Curiously, it casts Archeology in a role very similar to that of which Climatology is experiencing today in the 2010's -- a previously rather obscure wing of science is brought into the limelight of popular media and popular sentiment. This would have been the same thing that both rocketry and nuclear energy were experiencing in this 1930's-40's era. ...but not computers. <grin>
...Yeah this is good technofiction. Miller is doing a nice twist on both time travel and human thinking about it.
The problem of getting enough exercise if you're a brain worker was around even then.
A cute twist: it's an object that cycles through a time-loop, not a person.
I'd forgotten the details of this story, but now that I've read it again, I remember them, and I liked the story.
One small inconsistency comes to mind: Whatever caused grandpa's death from his visiting the site thirteen minutes or so earlier -- virus or whatever -- does not show up for grandson.
Second inconsistency: Grandpa Walter did not reveal to grandson that he'd found his own museum. ...Odd, but possible.
Two thoughts hit me a bit after reading: Even though this time travel is only to the future we can still have paradox. First, there could have been, and should have been, many people time traveling to the museum at discovery time to pay homage. They would have interacted with Walter. An obnoxious form would have been dozens of media crews there jockeying to interview him on-the-spot about his discovery. A more discrete version would be dozens of survelliance devices of various sorts from various times hidden around the site.
Second, the knife should have been stolen time and time again over the years -- perhaps stolen and replaced routinely by time bandits and time marshals. Some of the stealers would be motivated by profit, but many would be motivated by advertising a protest -- terrorists.
In sum, a time loop, such as this knife is, is also subject to paradox issues even if it can only be accessed from the past. So the story is neat, but the premise is not quite solid. It becomes an interesting exploration just for that reason.