Note that in spite of the "Vaseline" name this product does not contain petroleum jelly. It is instead plain old mineral oil (henceforth abbreviated POMO) with some "fragrance" added. The fragrance can only be described as smelling like the 1940's. If you thought Old Spice smelled dated, you ain't smelled nothing yet.

Vaseline Hair Tonic goes way back. Google for it, and most of the hits are for people buying/selling/discussing collectible advertising. I'm not sure when it was introduced, but it was definately pre-WWII.

The effect of putting mineral oil in your hair is pretty much what you'd expect. You know how if you go a long time without washing your hair, your natural body oil (sebum, I think its called) eventually builds up and makes the hair greasy to the touch (well, that happens to some people anyway)? A moderate amount of Vaseline Hair Tonic is basically a way to achieve that oiliness instantly, allowing you to wash your hair everyday and still look like you didn't. In larger amounts it is really shiny, too. It basically never dries out, either. All day long your hair will be slick and slimy. And so will your scalp, which is exactly what I wanted from this product. Another advantage is, if for any reason you ever want to get some mineral oil on your hands, you can just run them through your hair.

There are two main disadvantages. One is that if you have a bald spot like me, be extra careful about going out into the sun. POMO is (in)famous for its ability to act like a magnifying glass for the UV rays and really fry your skin. (cf. the way a lot of women use baby oil, or at least used to before people found out about skin cancer).

The other drawback to this product is that it provides almost no 'hold'. It's pure slickness without the control that one normally associates with products such as creams and pomades. If you want the shine and the smell of Vaseline Hair Tonic but also want to be able to keep your hair in place like a 50's TV dad, you need to use it in conjunction with something else. (I think this is what Elvis did, btw)

Petroleum Jelly was apparently the adjunct of choice in the 50's and still works pretty good for this now. See also the comments about getting it on your hands, too. A lot of the more complicated hair products actually are based on a mixture of POMO and PJ, so this is really like rolling your own custom hair gel and letting you control the relative amounts yourself.

(Side note: petroleum jelly is apparently the real "greasy kid stuff" of the 50's. It's what young guys would put in their hair when they needed lots of cheap goop and couldn't afford pomade. Plain PJ offers plenty of hold (not as much as wax) but very little shine and it of course smells like... well, PJ. There is also a product called Tres Flores, apparently aimed at hispanic men, which consists of PJ and very strong cologne. My wife would probably kick me out of the house for using it).