Henri Becquerel, discoverer of spontaneous radioactivity, arrived at the correct explanation for the mysterious phenomenon of intense images left behind from uranium salts on photographic plates kept in the darkness of a bureau drawer in May of 1896: it was, in fact, penetrating radiation.
The bottom photo clearly shows Becquerel’s photographic plate which had been fogged by radiation exposure from a uranium salt. The shadow of a metal Maltese Cross placed between the plate and the uranium salt is clearly visible.
Fog in a creek bottom near Pernell, Oklahoma back in the Winter. This type of fog is known as radiation fog and it forms when the air near the ground becomes saturated as warm air from the ground rises into it.