Not long ago I was having a conversation with a friend of mine and we were discussing what seems to be an out of place object in The Canon. It can't be an anachronism as it was written into the text during the time it was supposed to be taking place. If it were a newly written case and mentioned an electric refrigerator at 221b, that would be an anachronism. In this case, however, the term "tennis shoes" only seems out of place.
In CHAS Holmes is going over the equipment he has for the break-in at Milverton's and asks to make sure Watson has the correct footwear for such an endeavor.
"This is a first-class, up-to-date burgling kit, with nickel-plated jemmy, diamond-tipped glass cutter, adaptable keys, and every modern improvement which the march of civilization demands. Here, too, is my dark lantern. Everything is in order. Have you a pair of silent shoes?"
"I have rubber-soled tennis shoes."
The ultimate point of my work here at Historical Sherlock is to find ways to help date the stories. I am always looking for things that help confirm that The Game is not in vain, and that it is possible that The Dynamic Duo actually walked this earth. Unfortunately, the only conclusion we can draw here is that Watson wasn't out of place and time when he mentioned "rubber-soled tennis shoes" and that once again The Canon is correct about something. It can't help in our dating of CHAS or any other case, but at least now we know we can eliminate this from the list of those things.