After Nikola Tesla gave a lecture before the Royal Institution in London, he became very good friends with British scientist Sir William Crookes who was in attendance at the lecture. The next day, Crookes invited Tesla to his laboratory where Tesla showed Crookes how to build Tesla Coils on his own. They would have dinner that night and converse over a wide range of topics such as their own research, the importance of electricity in the future, metaphysics, religion, and even some of Crookes experiments which involved mental telepathy, spiritualism and human levitation. Crookes would notice Tesla's poor health from overwork, and after Tesla's departure would write him this letter:
My dear Tesla,
You are a true prophet. I have finished my new coil, and it does not do so well as the little one you made for me. I fear it is too large. I have fitted it with two sets of Levden jars; six quart jars on each side, but the spark is not long or thick, and there is scarcely any brush to be seen. The phosphorescence through my body when I hold one terminal is decidedly inferior to that given with the little one. I am actuating it only with the ordinary make and break of the large coil, as the alternator is not yet here, I do not think I have made any mistake in the winding of the coil, as your coil does just the same as mine.
I hope you will get away to the mountains of your native land as soon as you can. You are suffering from over work, and if you do not take care of yourself you will break down. Don't answer this letter or see any one but take the first train. I am thinking of doing so myself, but I am only thinking of going as far as Hastings.
With our united kindest regards,
Believe me,
very sincerely yours,
William Crookes.










