When you press "Enter" after typing text in a Tumblr post, the service automatically creates a paragraph break; however, subsequent spaces are ignored even if you press "Enter" multiple times. The only way to add more spaces below text is by inserting line breaks manually while viewing the HTML source of the post. The space between individual posts is defined by the theme, but some themes -- such as Strict and Panda Classics Recycled -- feature no spaces. To add a space below posts when using these themes, you must edit the HTML of the theme.
Adding Spaces Between Lines of Text
Sign in to your Tumblr account, and then click the "Text post" button on the Dashboard.
Type a title for the post, and then type the contents of the post.
Click the "<HTML>" button to view the HTML source of the post.
Type " " (without the quotation marks) on a new line between the sentences where you want to add a space. Each " " tag you insert adds a new line of space between your sentences.
Click the "Post" button to create the post with the lines of space you inserted.
Adding Spaces Between Posts
Sign in to your Tumblr account, and then click the "Customize" button.
Click "Edit HTML" to view the source code of the selected theme.
Press "Ctrl-F" to open the search box, type ".post" (without the quotation marks), and then press "Enter" to jump to the ".post" section of code.
Insert a new line, and then type "margin-bottom:40px;" (without the quotation marks). Replace "40px" with the size in pixels that you want the space between posts to be.
Click "Update Preview," and then click "Save" to save the changes.