On the Dashboard
While logged into Tumblr, click the gear icon to visit your customizations page. Select the “Dashboard” tab, and then check the box next to “Enable Endless Scrolling.” Click the “Save” button to save your changes. When you next visit your Tumblr dashboard, it will automatically load the next 10 posts after you scroll past the first 10. Because so many posts on Tumblr are media-heavy, endless scrolling can be resource-intensive on older computers and may cause your dashboard to load more slowly.
On Your Blog
To enable endless scrolling on your blog, you must first install a theme that enables the feature. You can see which native Tumblr theme includes endless scrolling by browsing the theme gallery (link in Resources) and then clicking the thumbnail of the theme. The theme’s description usually notes if it includes endless scrolling. You can click “Install” on a free theme, or “Purchase” on a premium theme, to add it to your Tumblr.