Peter Barlow to Faraday   14 March 1822

Royl Mily Acady March 14th | 1822

Dear Sir

You will be pleased to hear how well I have succeeded in the construction of my new galvanic apparatus, which in its present form does everything I can wish. I have repeated all your very interesting rotating experiments, and have added one very curious one, which although it throws no new light on the subject is very interesting in the exhibition. I enclose you a drawing of the machine[.]

AB is a piece of wood, CD a stout brass or copper wire; abcd a rectangle of smaller wire soldered at E; W is a light pointed copper wheel, the lower teeth of which are slightly immersed in the reservoir of mercury fg: hi is a channel of mercury merely for making the contact and HM a pretty strong horse shoe magnet, which of course may be supplied by two bar magnets. The mercury being now poured into the reservoir and the contact made at D and at i; the wheel begins to rotate, with an astonishing velocity, and thus exhibits a very pretty appearance-

I have some other experiments in progress which if they succeed to my mind I will inform you of; and when I have got through these I shall proceed to examine the effects with reference to their mathematical laws in which I have some hopes of success¹. I have repeated the copper cylinder experiment which you showed me when I had the pleasure of seeing you and found it to answer admirably.

I hope you and Mrs Faraday will bear in mind your promised visit to Woolwich during the Easter recess - pray make my compliments to Mrs F, and believe me

Dear Sir yours | very Truly | P. Barlow

P.S. I enclose you a little of the powder I mentioned when I saw you; if you can find an opportunity of examining it I should be glad to know the result for the satisfaction of my assistant who is a very ingenious fellow[.]

Endorsed by Faraday: Is sulphate of copper with a little charcoal - is soluble in water (nearly all of it.)