In the early 1950's, these types of books were popular. lately, in the 2000's, there is controversy about two different types of UFO sightings, solid Ships like shown below & bright lights, also shown below.

Apparently, the smaller bright lights were coming out  of or going into the larger cigar shapes ship. 

One of my hobbies is collecting all the books written by the well known authors.

It's a fascinating trip in time. Abebooks.com or other used book internet sites sometimes ave these books for  a dollar or two, including cheap shipping.