1920s marine transmitting books w/illustrations National Radio Institute

Lot of two old 1920s books from the National Radio Institute -Complete Course in Practical Radio-. There is:

Marine Spark Transmitting Apparatus (copyright 1926). This has 30 pages with drawings and schematics. We've been told the a spark transmitting device was the earliest practical radio system and was the type that radio and wireless communication pioneer Marconi used in his work.

There is also Marine Tube Transmitting Apparatus (copyright 1927). This has 28 pages with lots of schmatics and photos.

These have some surface soil to the covers from years in storage in an attic.

this item no longer available
Item No. k44528