I figured out the tubular cast on! Thanks to part 1 and part 2 of this video.
To cast on, I used a very long straight needle. (Thank you for the needles, Aunt Ellie!) As you can see, I kept the needle upright. And, when I knit the swatches, I tucked one needle under my arm.
Here are the swatches. The left one is the long-tail cast on. The right one is the tubular cast on. Something seems off and I'm not sure I like the look of it. Several people have suggested that I should try Eunny's tubular cast on and I will.
One more thing. The blue (almanac) yarn was asking to be something else. Thank goodness I have more Shelter yarn in hayloft to make the scarf!