[TYPOGRAPHICAL ERRORS CORRECTED]
The following typographical errors in the text were corrected as detailed here.
In the text: "It was only necessary to dampen these sponges to ensure a perfect discharge of the electrical current passing through the head-rest ..." the word "ensue" was corrected to "ensure."
Some hypenation was inconsistently used in the original. These have been retained as they appear in the original text.