William Jennings, Pioneer Work in Photography of Lightning, 1930

Something to Prove

Jennings set out to prove that the wind was the cause of the ribbon effect in a laboratory of the University of Pennsylvania, under the direction of Professor Arthur Goodspeed. To test Jennings' theory, the two scientists blew a blast of air across the direction of a single spark from an induction coil, resulting in the image shown here:

In a letter to Franklin Institute Secretary Hoadley, Jennings claimed that the "Ribbon Effect" was his own original observation.

You can view the original letter penned in Jennings' elaborate scrawl by clicking on the thumbnail at right. Find a transcription of the letter below*.

Jennings also proved that a lightning flash does not confine itself to one plane. In order to demonstrate this fact, he placed two similar cameras one-hundred feet apart, and succeeded in obtaining two negatives of the same discharge. The plate at right shows the results of his experiment, which were displayed publicly for the first time at a convening of the members of The Franklin Institute in May of 1892.

My Dear Doctor:

Referring to our conversation on lightning today:

I would refer you to the Journal of the F.I. Jan. 1892 p. 77

So far as I know the following observation is original with me:

"When lightning has once opened up a path in space there usually follows immediately along the same line a series of discharges. If the camera be moved across its path, the resulting photograph is liable to show a series of parallel ribbons of lightning, which has given rise to the opinion that it is not an instantaneous flash."

Since that time I have seen and caught these "ribbon" flashes, some made by moving the camera across what to the eye looked like a single flashes, others by the wind moving the path of the original discharge.

Sincerely,

W.N. Jennings

Jennings to Hoadley, 10/3/1929. (2.3M)

Report Plate 8. (188K)