What length of hair was Charles Nessler's heat permanent waving machine suitable for?

Charles Nessler's heat permanent waving machine was designed primarily for long hair. The construction and mechanism of the machine utilized heat and chemical solutions to create lasting curls or waves, which are more effectively achieved with longer strands of hair. Longer hair provides more surface area for the heat to work upon and allows for the formation of more pronounced styles. This machine was a significant advancement in hairstyling, particularly for those looking to achieve intricate waves, which were popular during the time Nessler introduced his machine.

Medium, short, and very short hair might not have been as compatible with the technique used by the machine, as it may not provide enough length for the heat and chemicals to achieve the desired curling effect effectively. Thus, long hair is the most suitable option when discussing the capabilities of Nessler's machine.