A couple more Tumblr questions...

I'm slowly getting the hang of it I think but I have two more questions:

1. When I search all of tumblr (not just one blog) for something like a tv show for example, is there a way to search tumblr based on upload date like on Youtube so it'll start with the very first posts about that topic and go from there instead of the most recent ones?

2. Can I post a comment on someone's post without reblogging it or do I have to reblog it and if I reblog it just to post my comment and then delete it from my blog will others still be able to see my comment?

Thank you for your answers! :)