If you see a blog post that you would like to comment on, click on the title of the post to see the item in isolation from the rest of the "blog roll" - a Comments box will appear underneath the item:
Type your Comment then click on the Comment As: Select Profile box.
Type your Name
Leave URL blank. Click on Continue.
Click on Publish.
Click in the little square to show that you are not a robot.
(A box may pop up with numbers or words for you to type to prove that you are not a robot.)
Click on Publish again.
Your comment will appear on the blog as soon as possible. It will be seen by clicking on Comments under the post you have commented on.
APS Members - To add a blog post please e-mail it, with a title, to email@example.com